Same goes with names: missing accents, umlauts, special characters, wrong ordering, wrong titles/gender etc. is aggravating. And customers do complain.
German companies often spend a non-trivial amount on software engineering time and data cleanup to get these things right. And the French take it even more seriously.
Non-native speakers may not understand it, but that's no excuse and you will alienate people and customers. Even younger generations notice.
And just fyi I'm a millennial and per "Du" with everyone I know. Not my telco provider though.