First of all lemme clarify - i solemnly believe this to be a general bug and NOT a translation error, that's why it's in the tech. issues forum.
It's about the engineer Variable Polarity talent. The tooltip clearly says that EVERY heating/cooling shot deals extra damage (if a debuff is present) and debuffs the target with cold/heat vulnerability which causes the next heating/cooling shot to do extra damage and debuff the target with cold/heat vulnerability and so on and so on. However, despite the talent's description either vulnerability debuff applies itself with about 20% chance per shot and as far as i can tell you can't apply consecutive vulnerabilities on a target.
I have 3/3 Variable Polarity and i've spent about 90 min testing this.
So this needs to either be fixed or the tooltip needs changing, because if it's working as intended variable polarity is utter shit.