I have installed todays V5 nightly and tried to start how it works from looking some demos.
But when in KiCad main window I tried to open any project by (File/Open Project…) I could’t find any *.pro files.
At the and I supposed they were not installed, but checking directly on disk I see them.
I found that if I change language from Default (means Polish) to English KiCad sees *.pro files.
I wonted to report a bug but it is there (#1740481). Looking through it I am suprised that they decided to not repaire it as it is up to translators.
I suppose (not sure) that project files has the extension .pro in all languages so in my opinion the problem of using *.pro filter in that window is not translators problem.
Please don’t jump to conclusions like that! It might be counter-intuitive, but the devs know their code…
The way translations are done is that kiCad strings are coded in English with a special macro. Those strings are then used as a “message id” in a translation file, where the translations are created, e.g. in this case the string is found here
You can see that the translations are incorrect, it adds an extra “.pro” so the Polish version will look for “*.pro.pro” Wayne changed the code to make the “.pro” non-translatable but many translation files have not been updated. Anyway, you could raise an issue at https://github.com/KiCad/kicad-i18n/issues. This was all mentioned in the bug report…if you read it.
I supposed that when I write “I suppose (not sure)” then my conclusion is weak enough.
It took me long time to understand why these translations are incorrect. The translations seemed for me more correct then origins .
I not always precisily understand what is written in English even if it is clear for others.
Now I suppose that decision to add .pro was betwean V4 and V5, and that way translations becomed incorrect.
I am probably the lat person to sey anything here, but may be it is posiible to modify the software that way that it will remowe from such string(s) all after ‘|’ and add *.pro. and may be all translations at once become correct even are incorrect This could be removed after all translations will be corrected but it gives more time for it.
You don’t know how long it took me to report my first bug. It was about an year. When I tried to setup an account they asked me to check that I have read and accept some ‘Rules’. I’m not the one who clicks everything without thinking. I have read and don’t understand that language. Some last paragraphs looked for me like it will/can cost me. I gave up. That sequence happened few times since January 2017 when I first time looked at KiCad. A month ago I gave-up and said - untill I will not give them my card number they probably will have no way to charge me (but who knows) and report #1774171 bug. If I read to raise an issue at some new place I am ill
Wayne changed the code to make the “.pro” non-translatable but many translation files have not been updated. Anyway, you could raise an issue at 
.