Here I am on a fully working Ubuntu 16.04 LTS and ordinarily I get no warning $ env|grep LANG LANG=en_US.UTF-8 $ fc-match sans DejaVuSans.ttf: "DejaVu Sans" "Book" But if I mimic having no locales : $ export LANG=UTF-8 $ fc-match sans Fontconfig warning: ignoring UTF-8: not a valid region tag DejaVuSans.ttf: "DejaVu Sans" "Book" So in other words if you don't install any locales on the system, fontconfig will issue this error. This came up in a minimal new install used for some testing. Perhaps a setting of UTF-8 should be silently ignored but a conclusion that fontconfig should always warn in this situation is fine by me, but I'd at least like to document it.
fontconfig warns because you set the invalid locale at the env var. not because it isn't installed on the system. see: $ LANG=xyz.UTF-8 locale locale: Cannot set LC_CTYPE to default locale: No such file or directory locale: Cannot set LC_MESSAGES to default locale: No such file or directory locale: Cannot set LC_ALL to default locale: No such file or directory LANG=xyz.UTF-8 LC_CTYPE="xyz.UTF-8" LC_NUMERIC=ja_JP.UTF-8 LC_TIME=ja_JP.UTF-8 LC_COLLATE="xyz.UTF-8" LC_MONETARY=ja_JP.UTF-8 LC_MESSAGES="xyz.UTF-8" LC_PAPER=ja_JP.UTF-8 LC_NAME="xyz.UTF-8" LC_ADDRESS="xyz.UTF-8" LC_TELEPHONE="xyz.UTF-8" LC_MEASUREMENT=ja_JP.UTF-8 LC_IDENTIFICATION="xyz.UTF-8" LC_ALL= $ LANG=xyz.UTF-8 fc-match DejaVuSans.ttf: "DejaVu Sans" "Book"
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.