Metric _and_ imperial.
TBH I did stop individually customising them early on. I had a whole mini library of application letters and targeted CVs. I just picked the closest and wanged it off.
For roles in Norway, Sweden, the Francophonie, Spain, and DACH, I wrote the cover letters in their language, then put it through Google Translate _into_ English to check I had not made howlers. I left my own errors as proof of human origin.
This had no detectable effect.