Compiere is designed to support the user interface in multiple languages - and to support multiple document languages. Example: the users of the system with English or Spanish windows/reports - while you are sending invoices (documents) to your customers in English, German and Russian.
Out of the box, Compiere provides the infrastructure for 28 languages including the two Chinese, Japanese, Thai, Spanish (and Mexian), as well as British and Australian. The language infrastructure is based on Unicode and handles all languages and dialects.
The bulk of the translation is exported and imported via XML files to allow the use of translation tools like Trados. Even though it might seem easier to "just translate" the system, you will realize significant savings for maintaining the translation with a translation tool - and the initial translation also will be less effort and with higher consistency.
Compiere at this very moment has about 106,000 words to translate. You can reduce that volume to about 98,000 if you only translate the parts a user of the system would see (i.e. not system administrator functionality). If you skip the translation of the Help text (i.e. only labels and bubble help), the word count is reduced to 46,000.
Compiere offers "Language Packs" which are a good base for a translation. Here I want to outline, what steps are necessary to create and maintain a Language pack efficiently: