User Translate is a Blender add-on that lets you add your own translated text to the interface, either manually or through a semi-automatic process. It turns the English text of external add-ons into the language of your own country, and it supports Blender versions 3.0 through 5.1 under a GPL license.
Translations are driven by a dictionary. Place a .csv file in the add-on's user_files folder and it will be read as a translation dictionary, using a two-column "Translated text","English" format you can edit in spreadsheet software such as Excel. An automatic update function reloads the dictionary every second, so translations show up immediately, and you can review the results on the Blender screen while editing the file in a text editor.
For larger jobs, User Translate can semi-automatically create translation files: export an external add-on's text as HTML, translate it in a browser, save the page, then convert it to CSV. Depending on the target add-on's structure, not all text may be extractable. A demo video is available.