How to switch language on pages containing charts created using Forena?
As per the "uncaught TypeError: $(...).dataTable is not a function" you mentioned, it sounds to me that what your language problem is actually not a language problem, but some installation issue related to what's required to Enable Data Tables support. I'd recommend you to first try to resolve that error (as explained in the documentation in the mink I mentioned before, which you can also find in your own site located at /reports/help.setup#datatables.

You may also want to look at my answer to the question about "How to translate the title, axis labels and legend of a chart?" for the typical steps required to correctly translate a chart create with Forena (just to make sure such translation exist for each of your languages, and that the URL for each translation of the report is correct, and does exist).

If neither of this helps to sort out what's happening, then please further enhance your question by including your report/chart specifications (= what's called the "frx"-source in Forena). After doing so, I'd be happy to try to further enhance my answer also.

Disclosure: I'm a co-maintainer of Forena Reports.