Using the option "Text configuration" under Settings > Hosted pages settings, the language of the text fields can be changed as desired in Chargebee.

Similarly, all editable fields in Chargebee can be translated/customized to any language of the user's choice.

Hers's a sample screenshot of the customer portal page:

Note -  Though all these editable fields can be customized to any desired language, the system messages error texts etc. would appear in English only.