I tried it here on my English OS Lion.. 7.2...
I removed ALL .lproj files except for de.lproj from the Resources folder of PT10...
PT 10 now boots into German
Try this (Either HAS to work)
1)
A) Command + Click PT Icon in Dock
B) right Click Protools > Select Show Package Contents
C) Navigate to Resources
D) Find and delete
de.lproj
es.lproj
fr.lproj
ja.lproj
ko.lproj
zh_CN.lproj
zh_TW.lproj
(MAybe just move them to Desktop so you can add them back later if you please
2) Scenario Two if 01 does not work
Same as above but rename en.lproj to de.lproj
3) 100 % Working Scenraio
A) Purchase
TinkerTool 2
B) Launch App and under System Settings choose 'Application Language'
C) Drop PT10 into the Application Drag Zone
D) On the right side under Language to Use - choose English
E) Click launch
This will boot the app into ANY language available...
Tinkertool System is GREAT for MANY things... I I wouldn't wanna be without it