@rimelek
If i extend my Dockerfile with
&& docker-php-ext-configure intl && docker-php-ext-install -j$(nproc) intl
i get
configure: error: Package requirements (icu-uc >= 50.1 icu-io icu-i18n) were not met:
No package ‘icu-uc’ found
No package ‘icu-io’ found
No package ‘icu-i18n’ found
Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.
Alternatively, you may set the environment variables ICU_CFLAGS
and ICU_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.
So please, like you and all other see, i need help! 
