The interlanguage links dashboard at https://language-reportcard.wmflabs.org/interlanguage/#desktop has been broken since November 4 2018. It shows no data for particular languages, but if you select all the languages, it shows a chart for a "null" language. We haven't looked at this dashboard for some time, but we may make changes in the products around interlanguage links in the foreseeable future, so it must be fixed.
I thought that it happened because of some change that we didn't notice in the wmf.projectview_hourly table. However, I cannot find anything broken in how the query runs at the moment. I tried running it and it seems to give sensible data.