Quick disclosure before the tutorial: I work at Cool Plugins, the team behind LocoAI, which is the AI translation addon this post centres on. WordPress has two completely different translation problems. One is translating your site content (posts, pages, products). The other is translating the WordPress interface itself (plugin labels, theme strings, button text). This post is about the second problem and how to solve it with AI in 2026.
The two-translation problem most guides skip
Site content (the article you are reading now, a product description, a contact page) lives in your WordPress database and gets translated by a multilingual plugin like Polylang, WPML or TranslatePress on top of an AI addon. Plugin and theme interface text (the "Add to cart" button, the "Settings saved" notice, the field labels in your form plugin) lives in .po and .mo files shipped inside each plugin or theme. Multilingual plugins do not touch those files. You need a different tool.
That tool is Loco Translate on its own for manual editing, and LocoAI on top for AI bulk translation. The combination handles every plugin and theme string in your WordPress install, including the WP admin itself.
What .po and .mo files actually are
Plugins and themes ship their interface text in .po files. It is a text format
from the GNU gettext project. The .po file lists every translatable string in
the plugin or theme along with its translation per language. When WordPress runs, it loads
the compiled .mo binary version for performance.
If you have ever seen a plugin where some buttons are in English and others in your language,
it is almost always a missing or incomplete .po file. Translate the file,
Loco Translate compiles the .mo automatically and the next page load shows the
UI in your language.
Loco Translate: the foundation
Loco Translate
is the WordPress plugin for managing .po and .mo files inside
your WP admin. Install it from WordPress.org, navigate to any plugin or theme and you get a
list of translatable strings with input fields per language. It is free, well maintained and
has more than a million active installs at the time of writing.
On its own, Loco Translate is a manual editor. You click each string and type the translation. That is fine for a 50-string plugin. For a 5,000-string theme like Avada, a complex WooCommerce extension or your entire WordPress admin in a new language, manual translation is simply not the right tool.
LocoAI: AI translation inside Loco Translate
LocoAI is our addon for Loco Translate. It adds AI translation buttons directly into the standard Loco interface, so the workflow stays exactly the way you already use it. You just get a "Translate with AI" option on every string plus a bulk translate action for handling thousands of strings at once.
LocoAI ships with five AI providers, two of them completely free with no API key required:
- Google Translate: free, unlimited, no API key. Built into LocoAI, no Google Cloud account needed. Best general-purpose first-pass for plugin and theme UI strings.
- Chrome built-in AI: free, unlimited, runs entirely in your browser. No API key, no quota, no data leaves your machine. Ideal for unreleased plugins, commercial themes and any privacy-sensitive translation work.
- OpenAI (your own API key): best for marketing-y plugin descriptions and onboarding text where tone matters.
- Gemini (your own API key): cheapest paid premium provider, generous free tier on Google AI Studio.
- DeepL (your own API key): best for European languages like German, French, Spanish, Italian.
The headline is the first two providers. You can translate an entire plugin or theme into multiple languages with zero ongoing cost using Google Translate or Chrome built-in AI inside LocoAI. No API keys, no monthly bills, no third-party translation services. That covers the majority of real-world plugin and theme translation work.
Bulk-translate .po files inside Loco Translate using Google Translate or Chrome built-in AI. Unlimited translation, no API key, no monthly cost.
The free LocoAI version on WordPress.org
LocoAI has a free version on WordPress.org with over 75,000 active installs. The free build ships with Google Translate and Chrome built-in AI ready to go, which means you can run the complete bulk translation workflow at zero cost from day one. The premium version unlocks OpenAI, Gemini and DeepL for teams that want higher quality on tone-heavy strings. The product page covers the full feature comparison.
Step by step: AI translate a plugin or theme with LocoAI
Full setup is about five minutes the first time. Every translation job after that is two or three clicks from the Loco Translate interface.
Step 1. Install Loco Translate and LocoAI
Install Loco Translate from WordPress.org. Install LocoAI alongside it (free or premium). Activate both. LocoAI detects Loco Translate automatically and hooks into its standard interface.
Step 2. Open LocoAI settings and pick a provider
Go to the LocoAI settings page in your WordPress admin. Pick a provider:
- For free unlimited translation: Google Translate or Chrome built-in AI. No API key required.
- For premium tone-aware translation: OpenAI, Gemini or DeepL. Paste your API key and save.
Most plugin developers and site owners I work with use Chrome built-in AI as the default. Free, offline, private, no quota. Switch to OpenAI only for the strings that really need tone polish (marketing copy, plugin descriptions, customer-facing messages).
Step 3. Navigate to the plugin or theme
In WordPress admin, go to Loco Translate then Plugins (or Themes). Pick the plugin or theme you want to translate. Loco shows you the available languages and any existing translations.
Step 4. Add a new language or open an existing translation
Click "+ New language" if your target language is not there yet. Pick the language and the file location (use the default "System" location so your translations survive plugin or theme updates). Loco scans the source code and shows every translatable string in a clean table.
Step 5. Run AI bulk translation
With LocoAI active, you will see a "Translate with AI" button in the toolbar. Click it. LocoAI sends all untranslated strings to your selected provider in batches and fills in the translations. Coffee break. For a 1,000-string plugin, the whole bulk pass usually takes a few minutes.
Step 6. Review and refine
Walk through the output, especially strings with placeholders, HTML or technical terms. LocoAI preserves placeholders automatically, but spot-checking the first dozen entries is good practice. Edit any string in place. Save when you are happy.
Step 7. Compile to .mo
Loco Translate compiles the .mo file automatically on save. Your translations
are live. WordPress will load them on the next request to that plugin or theme.
Picking the right LocoAI provider
A short decision framework:
- Default for everything: Chrome built-in AI. Free, unlimited, in-browser, no API key.
- If Chrome built-in AI is not available on your machine: Google Translate inside LocoAI. Also free, also unlimited, no API key needed.
- Marketing-heavy plugin descriptions or customer-facing UI: OpenAI with your own API key. Best tone of the five providers.
- High volume work where you still want premium quality: Gemini Flash. Roughly 10× cheaper than OpenAI for comparable quality on most language pairs.
- European-language theme or plugin (German, French, Spanish, Italian): DeepL with your own API key. Still the leader on those specific languages.
On real projects the most common workflow is Chrome AI or Google Translate for the bulk first pass, then OpenAI on the dozen or so strings that face the end customer (welcome messages, plugin description, onboarding flow). Total cost: zero for the bulk, pennies for the polish.
Where translations get stored
This is one of the more confusing parts of .po translation, so it is worth being explicit:
- Plugins (WordPress.org locations):
/wp-content/languages/plugins/{plugin-slug}-{locale}.po - Plugins (in-plugin locations):
{plugin-folder}/languages/for translations the plugin ships with - Themes:
/wp-content/languages/themes/{theme-slug}-{locale}.po. Themes often also ship their own in{theme-folder}/languages/ - Core WordPress:
/wp-content/languages/{locale}.pofor the WP admin itself
Loco Translate handles the location for you. The default "System" save location is
/wp-content/languages/, which means your translations survive plugin and theme
updates. If you save inside the plugin or theme folder instead, an update can overwrite
them. Stick with System unless you have a specific reason to save elsewhere.
Special cases that trip people up
Placeholders like %s, %d and %1$s
Strings like "Welcome back, %s!" use placeholders that get replaced at runtime.
The AI must not translate %s or change its position. LocoAI handles this
automatically and preserves placeholder order across all five providers.
HTML embedded in strings
Strings sometimes contain HTML, for example "Click <a href='%s'>here</a> to login".
LocoAI preserves the HTML structure and only translates the surrounding text. Other generic
AI tools may mangle the tags, so this is one of the practical advantages of using LocoAI
rather than copy-pasting through a chat interface.
Context strings (msgctxt)
Some plugins use translation context to distinguish identical strings with different meanings. Classic example: "Post" as a noun (a blog post) vs "Post" as a verb (to send). LocoAI passes context to the AI provider so it picks the right translation in each case.
Plural forms
Strings like "%d comment / %d comments" have plural forms that vary by language.
Some Slavic languages have five or six plural forms. LocoAI translates each form correctly.
You will see them as separate fields in Loco Translate's interface.
Common use cases for .po translation
Plugin developer shipping a multilingual plugin
You wrote a plugin. You want it usable in Spanish, French, German, Italian and Portuguese.
Translate your .po file via LocoAI using Chrome built-in AI (so unreleased
plugin source never leaves your machine), save to your plugin's /languages/
folder, ship the translations bundled with your plugin. Users in those locales get a
translated interface automatically the next time WordPress loads.
Site owner with a half-translated plugin
You are running a plugin and most of it shows in your language, but some strings (newer
features, less-popular plugins) are still in English. Load the .po file in Loco
Translate, run LocoAI on the untranslated strings using Google Translate or Chrome AI, save.
Site UI is fully in your language at zero cost.
Agency translating a client's WordPress backend
Client wants the WP admin in Japanese including all installed plugins. Loco Translate scans every active plugin and theme. LocoAI bulk-translates the missing entries. A few hours of work for what would otherwise take weeks of manual data entry. The cost stays at zero when you use the free providers.
Quick FAQ on .po translation
Will WordPress.org's translation team translate my plugin for me? Sometimes. If your plugin gets popular, volunteer translators may contribute through translate.wordpress.org. Do not count on it. Ship your own translations first and let volunteers improve them later.
Does AI translation hurt my plugin's quality? If you are shipping software, review the AI output. Modern AI handles UI strings well, but technical context (file paths, error codes, branded terms) sometimes needs adjustment. Treat AI as a first draft, then skim the customer-facing strings before release.
Can I translate WPML, Polylang or TranslatePress's own admin strings this way?
Yes. All three ship .po files for their own UI. Translate them via Loco
Translate plus LocoAI just like any other plugin.
The bundle covers LocoAI for plugin and theme strings plus AutoPoly, AutoMLP and AutoTP for site content translation. One license for the full multilingual stack.
Wrapping up
Site content and plugin or theme UI strings are two different translation problems with two different toolsets. For UI strings (anything inside a plugin or theme), LocoAI on top of Loco Translate is the cleanest workflow. The free version on WordPress.org with 75,000+ active installs ships with Google Translate and Chrome built-in AI included, both completely free and unlimited. That covers the majority of real-world .po translation work without spending anything on API keys or third-party services.
For site content (posts, pages, WooCommerce products, custom post types), the matching workflow lives elsewhere. The WPML AI translation guide, the Polylang AI translation guide and the TranslatePress AI translation guide each cover that side end to end. If you are still deciding which multilingual plugin to use, the three-way comparison is the right starting point.
