I suspect 99% of the replies on here have missed the overriding law in aviation.
Its referred to as 'tombstone safety'. Nothing changes until there are deaths and it costs more in insurance payouts than to fix the problem.
How much would it cost, apart from the dint in nationalistic pride, for it to be compulsory for English to be used at one of the busiest airports in Europe. Let's remember standard RT phraseology does not mean having to be fluent. Indeed if you said 'QNH' to a typical Englishman you might as well be talking Mandarin. How hard can it be?