I've made a few similar changes (although not the French to US English) using Navtweek II in a customised V28 and all works fine.

I think all your planned changes have been done before and are documented here. Make sure you use the female voices only - don't try the male files as these are much older and smaller.

I changed "Memorise Veh. Position" to "Memorise X3's Position"

Be careful with the sky - I changed mine to a better resolution image but ended up with a broad white band for the horizon - the colour change from blue (top) to light blue to white (bottom) must be similar to the BMW standard sky image to avoid this problem.