You can buy Enterprise Architect in four language versions: Japanese, German, Spanish and English. These give you user-interface text (menus, dialogs, messages) in the appropriate language.
You can type in any user-entered text in whatever languages your keyboard supports. However, if your language uses special characters (as Polish, Chinese and Arabic do) then you must use a DBMS repository or set JET 4.0 as the db engine.
Apart from built-in spellcheck dictionaries for English in the US, British and Canadian flavours, EA has a downloadable file that provides spellcheck dictionaries for the Swedish, Spanish, Italian, Brazilian Portuguese, Dutch, French and German languages. This information is on the registered users website, but I have just added it to the 'Use Languages Other Than English' page in the Help topics on the Spellchecker.