I think the problem is due to the special characters in the file. I had the same problem and was able to change the language value using a hex editor instead of a normal text editor.
Thanks so much!
After much searching in the ini file I finally found the right lines to edit to fix the terrible mouse sensitivity with the hex editor!
For anyone interested there is 2 sets of lines as follows (I edited both so that the vertical min and max matched the horizontal min and max):
I left the defaults as they were - you can adjust the sensitivity in game just fine with the sliders, otherwise the game will freak out if the file length is longer or shorter than it was originally.
Why isnt THIS at the PCGamingWiki article?!
For anyone who finds it in the future: to get rid of this bad vertical sensitivity:
1. Set the values above in "Stranglehold\StrangleholdGame\Config\PC\Cooked\Coalesced.ini"
2. Load into the game and on some level
3. Open settings
4. Set your horizontal sensitivity to your desired preference and count how many "clicks" it took
5. Set your vertical sensitivity to half of what you've just set horizontal to (it's easier to count half the "clicks" of above)
6. Profit from 1-to-1 aiming sensitivity