Translation issue

Thanks for this beautiful theme.
My website is intended to a french audience, so translation is important.
I test this theme on a local website. I downloaded « Sorbet » from my 4.4.2 wordpress installation. Just to let you know that i had to rename « fr.po » to « fr_FR.po » and « fr.mo » to « fr_FR.mo » to get it effectively translated. These files are supplied in /wp-content/themes/sorbet/langages.
Is that due to a change in naming policy in WordPress ? Could it be corrected upstream (i would like to use this theme in a WordPress network) ?
Greetings
Herge