This plugin adds 30 languages to TinyMCE Advanced: Arabic (ar), Belarusian (be), Bokmål Norwegian (nb), Bulgarian (bg), Catalan (ca), Simplified Chinese (cn), Czech (cs), Danish (da), Dutch, Flemish (nl), Farsi (fa), Finnish (fi), Galician (gl), Greek (el), Hebrew (he), Hungarian (hu), Indonesian (id), Central Khmer (km), Korean (ko), Latvian (lv), Lithuanian (lt), Macedonian (mk), Norwegian (no), Polish (pl), Romanian (ro), Slovak (sk), Slovenian (sl), Swedish (sv), Turkish (tr), Ukrainian (uk), Welsh (cy).
If you have set WordPress to one of these languages and this plugin is enabled, the TinyMCE Advanced plugin will use that language for all buttons and popups added to the Visual editor.