There is the old Internationalization Add-On https://www.concrete5.org/marketplace/addons/internationalization... but has been deprecated and is now built-in to any version past 5.7.

It's already built in! Just type Internationalization into your concrete5 toolbar.

You may also wish to check that the issue isn't with your computer language settings.

It might be something to do with breaking text (string) with invisible characters, e.g. '\n\r' and/or space which somehow get combined with the first letter on the next line giving the wrong symbol.

With me it mostly happens in emails from forms where I use a lot of '\n' and '<br />' to construct email text in both plain text and html and in some blocks where I truncate and join strings.

Sometimes it just happens in the first email from the form within a certain period, and all other sent emails are fine. No idea why that happens.