. To clarify, are you using a French language keyboard, with an AZERTY layout enabled?
I wanted to let you know that the keyboard shortcuts are currently optimized for English-language keyboards.
The thing is, if the 'french' shortcut doesn't work, I should at least be able to use the english one. That is, if [ - ] is not remapped to the french version, the same physical key should work.
In Axure 8, the shortcut for decreasing font size was CTRL + SHIFT + [ < ]. For me it was an other key than [ < ] but it worked nonetheless.