I had to add using namespace icu;
to source/lib/external_libraries/icu.h
with icu 61 or else class Locale is not found.
I hate icu, each update breaks everything
@AudaciousTUX is also experiencing the issue, but adding the line mentioned above by itself doesn't fix it:
../../../source/i18n/L10n.cpp:517:24: error: expected type-specifier before ?Locale?
Locale* locale = new Locale(Locale::createCanonical(localeCode.c_str()));