When translating subtitling formats like SRT, the Linguist can see timing of the respective subtitles, but no information about the suitable length of that subtitle. There is no bulletproof method to ensure that the translation fits the ideal CPS (characters per second) ratio.
Available workaround (if any):
Setting up the max. length QA check, but that does not work for every case and/or language combination. Outside subtitling software is often needed to use for checking.
Add a QA check which would warn about exceeding number of characters in the target text for the individual segment/subtitle.
There is a standard of how many CPS (characters per second) should be in translation of individual subtitles. Possibility to set up the limit connected with QA check would help keeping the subtitles in the line of this standard.