What GPL compatibility is needed? The GPL has been brought to court twice in Europe (both times Germany) and it was upheld both times.
One motivation for the EUPL is that many governments cannot publish software under a licence that isn't one of their official languages. With the EUPL, the Swedish government can use the Swedish version, and downstream recipients can change the software to GPLv3. In that way, the EUPL can work as a shim, much easier than trying to translate the GPL into 23 languages.
Translating the GPL was considered during the GPLv3 process, but the stakes are enormous, and with licences like the EUPL and CeCILL which can act as a shim, translating the GPL isn't so important.