If you have customers in different countries and want to invoice in their language you can create a new language by simply changing any language name in Text & Translations.

• Open Text & Translations
• Select any language
• Edit the language name
• Click on save (then close and reopen the window)

you will see that a new language has been created! 

You can also use this method to apply different separators for thousands and/or decimals, regardless the Invoice template you use. Just create the language and link the new language to the Client / single Invoice to use different separators.