Created attachment 124048 [details]
the full before and after project diff

STEPS TO REPRODUCE
1. Set the Windows UI to pt_BR.
2. Make sure LC_ALL is not set, open a project saved with decimal commas, this will work
3. Set 'LC_ALL=pt_BR.UTF-8'
4. Reopen the project

OBSERVED RESULT
clips in timeline will be misaligned, some saved effects will stop working

EXPECTED RESULT
Same as if LC_ALL was not set. It is the same locale after all

SOFTWARE/OS VERSIONS
Windows: 10.0.18362.476

ADDITIONAL INFORMATION
I have LC_ALL=pt_BR.UTF-8 so git properly shows characters with accents in git logs, but when I have it set and try to open a project that was saved with my locale it gets all messed up.

Likewise, if I unset LC_ALL and open the projects I manually converted to decimal point (at first I thought it happened because I updated to 19.08.3), the same problem happens. However if I set LC_NUMERIC=C in the environment, or change kdenlive:docproperties.decimalPoint to '.', they work again.

I diff-ed my project before and after the breaking change:

-<mlt title="Anonymous Submission" LC_NUMERIC="pt_BR" producer="main_bin" version="6.16.0">
+<mlt title="Anonymous Submission" LC_NUMERIC="pt_BR.UTF-8" producer="main_bin" version="6.17.0">
  <profile frame_rate_num="30" sample_aspect_num="1" display_aspect_den="9" colorspace="709" progressive="1" description="HD 720p 30 fps" display_aspect_num="16" frame_rate_den="1" width="1280" height="720" sample_aspect_den="1"/>
- <producer title="Anonymous Submission" id="producer0" in="00:00:00,000" out="00:02:40,600">
+ <producer title="Anonymous Submission" id="producer0" in="00:00:00.000" out="00:02:40.000">

So it picked up LC_ALL from the environment, but it also changed all 'in' and 'out' timestamps to decimal points and lost the milliseconds, which explains the misaligned clips. :/