Under  Settings -> Invoice -> Text Translations, you may enter translations of invoice fields to generate invoices in your own language.

Your time entries are printed on invoices as they were entered, hence, no further translation is needed. At present translations only apply to simple PDF invoice format.

Note: In some languages, translations are much longer than default English terms. If your translation is longer than the default English term, the invoice may be deformed. Therefore, you should limit the translated terms to approximately the same width as the default English text.