Hoy dia es dificil que una distro no soporte TODOS los lenguajes, porque una distro es un proyecto que empaqueta programas, entre otras cosas, y empaqueta otros proyectos como gnome y kde, que tienen sus propios esfuerzos por traducir todo. En kde por ejemplo, tienes para elegir el idioma que mas rabia te de:
kjuanlu@eudytes:~$ apt-cache search i18n | grep kde
gettext-kde - version of gettext used by KDE
kde-i18n-af - Afrikaans internationalized (i18n) files for KDE
kde-i18n-ar - Arabic (ar) internationalized (i18n) files for KDE
kde-i18n-az - Azerbaijani internationalized (i18n) files for KDE
kde-i18n-bg - Bulgarian (bg) internationalized (i18n) files for KDE
kde-i18n-bn - Bengali (bn) internationalized (i18n) files for KDE
kde-i18n-br - Breton (br) internationalized (i18n) files for KDE
kde-i18n-bs - Bosnian (bs) internationalized (i18n) files for KDE
kde-i18n-ca - Catalan (ca) internationalized (i18n) files for KDE
kde-i18n-cs - Czech (cs) internationalized (i18n) files for KDE
kde-i18n-cy - Welsh (cy) internationalized (i18n) files for KDE
kde-i18n-da - Danish (da) internationalized (i18n) files for KDE
kde-i18n-de - German (de) internationalized (i18n) files for KDE
kde-i18n-el - Greek (el) internationalized (i18n) files for KDE
kde-i18n-engb - British English (en_GB) internationalized (i18n) files for KDE
kde-i18n-eo - Esperanto (eo) internationalized (i18n) files for KDE
kde-i18n-es - Spanish (es) internationalized (i18n) files for KDE
kde-i18n-et - Estonian (et) internationalized (i18n) files for KDE
kde-i18n-eu - Basque (eu) internationalized (i18n) files for KDE
kde-i18n-fa - Farsi (Persian) internationalized (i18n) files for KDE
kde-i18n-fi - Finnish (fi) internationalized (i18n) files for KDE
kde-i18n-fr - French (fr) internationalized (i18n) files for KDE
kde-i18n-fy - Frisian (fy) internationalized (i18n) files for KDE
kde-i18n-ga - Irish Gaelic (ga) internationalized (i18n) files for KDE
kde-i18n-gl - Galician internationalized (i18n) files for KDE
kde-i18n-he - Hebrew (he) internationalized (i18n) files for KDE
kde-i18n-hi - Hindi (hi) internationalized (i18n) files for KDE
kde-i18n-hr - Croatian internationalized (i18n) files for KDE
kde-i18n-hsb - Upper Sorbian (hsb) internationalized (i18n) files for KDE
kde-i18n-hu - Hungarian (hu) internationalized (i18n) files for KDE
kde-i18n-is - Icelandic (is) internationalized (i18n) files for KDE
kde-i18n-it - Italian (it) internationalized (i18n) files for KDE
kde-i18n-ja - Japanese (ja) internationalized (i18n) files for KDE
kde-i18n-kk - Kazakh internationalized (i18n) files for KDE
kde-i18n-km - Khmer internationalized (i18n) files for KDE
kde-i18n-ko - Korean internationalized (i18n) files for KDE
kde-i18n-lt - Lithuanian (lt) internationalized (i18n) files for KDE
kde-i18n-lv - Latvian internationalized (i18n) files for KDE
kde-i18n-mk - Macedonian (mk) internationalized (i18n) files for KDE
kde-i18n-mn - Mongolian internationalized (i18n) files for KDE
kde-i18n-ms - Malay internationalized (i18n) files for KDE
kde-i18n-nb - Norwegian Bookmal (nb) internationalized (i18n) files for KDE
kde-i18n-nds - Low Saxon (nds) internationalized (i18n) files for KDE
kde-i18n-nl - Dutch (nl) internationalized (i18n) files for KDE
kde-i18n-nn - Norwegian Nynorsk (nn) internationalized (i18n) files for KDE
kde-i18n-pa - Punjabi (pa) internationalized (i18n) files for KDE
kde-i18n-pl - Polish (pl) internationalized (i18n) files for KDE
kde-i18n-pt - Portuguese internationalized (i18n) files for KDE
kde-i18n-ptbr - Brazilian Portuguese (pt_BR) internationalized (i18n) files for KDE
kde-i18n-ro - Romanian (ro) internationalized (i18n) files for KDE
kde-i18n-ru - Russian (ru) internationalized (i18n) files for KDE
kde-i18n-rw - Kinyarwanda internationalized (i18n) files for KDE
kde-i18n-se - Northern Sami (se) internationalized (i18n) files for KDE
kde-i18n-sk - Slovak (sk) internationalized (i18n) files for KDE
kde-i18n-sl - Slovenian (sl) internationalized (i18n) files for KDE
kde-i18n-sr - Serbian Cyrillic (sr) internationalized (i18n) files for KDE
kde-i18n-srlatn - Serbian Latin (sr@Latn) internationalized (i18n) files for KDE
kde-i18n-ss - Swati internationalized (i18n) files for KDE
kde-i18n-sv - Swedish (sv) internationalized (i18n) files for KDE
kde-i18n-ta - Tamil (ta) internationalized (i18n) files for KDE
kde-i18n-tg - Tajik (tg) internationalized (i18n) files for KDE
kde-i18n-tr - Turkish (tr) internationalized (i18n) files for KDE
kde-i18n-uk - Ukrainian (uk) internationalized (i18n) files for KDE
kde-i18n-uz - Uzbek internationalized (i18n) files for KDE
kde-i18n-vi - Vietnamese internationalized (i18n) files for KDE
kde-i18n-zhcn - Chinese Simplified internationalized (i18n) files for KDE
kde-i18n-zhtw - Chinese Traditional internationalized (i18n) files for KDE
Y fuera del entorno grafico tambien se puede castellanizar, las paginas man, etc.... Ademas el ingles está muy bien