I have found that Japanese language support for the database server has been dropped for 10. This is because it fell below the 80% of strings translated requirement, so it was shipped without Japanese. This isn't true of all components, but it seems quite alarming that we've pushed out PostgreSQL 10 with no language support for a country that has contributed a significant amount to the project, and has a relatively large number of users.
The database server also dropped support for Indonesian and Portugese (Brazil). In fact, just between 9.6 and 10, the following language support was dropped for these components:
cs | plpython de | pg_resetxlog es | pg_resetxlog fr | pg_resetxlog id | postgres it | pg_resetxlog ja | pg_basebackup,pg_resetxlog,plpython,pltcl,postgres,psql ko | pg_resetxlog pl | pg_resetxlog pt_BR | pg_basebackup,pg_resetxlog,pltcl,postgres ru | pg_resetxlog sv | pg_resetxlog tr | plperl zh_CN | pg_basebackup,pg_resetxlog,pltcl zh_TW | plperl
This is a huge amount of compared to what happened between 9.5 and 9.6:
cs | pg_basebackup,pg_resetxlog ja | pg_basebackup,pg_resetxlog zh_TW | pg_ctl,postgres
There are many translations that are on the verge of falling under 80%. Japanese alone has 6 components between 80-83%, but other languages are in a similar position.
I feel this is something that we, as a community, need to address. Unfortunately, some of us aren't in a position to contribute to such an effort. We need folk to step forward to help get these translations updated, or this situation will likely only get worse.
I'll try to fix cs part. Some components are not too important for us - but psql and pg_basebackup should be translated. Probably there are zero users of pltcl and few users with plpython (but these users usually prefer English lang).