The other obvious European country that could have this problem is Switzerland, but they solved it in a completely different way.
Rather than trying to fit four official languages on the coins, they use one that is neither official nor used in daily discourse by anyone in Switzerland: Latin. You could argue that a possibly subconscious reason for why UK coins are still in Latin is similar. The disparity in number of speakers between English and the Celtic languages, plus the fact that the latter are only official in the countries of the UK where they are spoken natively, means the problem is less acute, but it is nonetheless there in the background.
Another solution is South Africa's, where there is a huge number of official languages. There they have opted to change the language(s) on any given denomination each year. For this to work, you have to be relatively certain before you start that you are going to have a series of types that will last long enough for all languages to get a fair crack at the whip (you're looking at 15-20 years in SA including time for the coins to actually be used). The community representatives concerned need also not to be so childish as to bicker about which order the coins are issued in or whether when a denomination is phased out the community whose language appeared last feels hard done by or whatever. The South Africans, at least back in the 90s, were more concerned with general freedom than such petty arguments; I'm not so sure the Belgians of either kind would see it the same way.