TeamViewer tries to determine the language for emails by using a best-guess heuristic. Among the options to choose from are the language in which you originally created your account, and the language of your last successful login.
Set up a fixed language
If you always would like to receive emails in a certain language you can choose the Email language in the Profile settings of the TeamViewer Management Console.
Note: If the language is not available for an email, the mail will be send in English by default. We are always working on making all emails available in all languages.
Note: All Remote Management emails alerts will be sent out in English only regardless of language setting.
Note: All emails to invite someone to create a TeamViewer Account are currently available in English and German only.