Alphabet letter collation order should be based on content language, not UI language

[osma]

At which URL did you encounter the problem?

http://finto.fi/yso/en/
http://finto.fi/yso/fi/?clang=en

What steps will reproduce the problem?

1. Look at YSO front page using either English UI or Finnish UI
2. Select English as content language

What is the expected output? What do you see instead?

Expected that in both cases the collation should follow the content language, i.e. the letters Å and Ä should be grouped with A. Instead the collation order seems to be based on the UI language, since with the Finnish UI the Finnish collation order is used (with Å Ä Ö at the end) regardless of content language.

[osma]

The problem is the usort with strcoll here. The sorting is done with the locale language, which means UI language.

[osma]

I think the collation should be moved to the SPARQL query side, where we have a way (at least with Jena Fuseki) of performing locale-specific collation. Using strcoll on the PHP side would require having locales installed for all the content languages and knowing the full names of those locales (e.g. en_GB.utf8 for content language en). We have that information only for the defined UI languages...

[osma]

Not sure if it's worthwhile to spend more time on this right now. However, I pushed a failing unit test on this branch which may be used later if so decided: https://github.com/NatLibFi/Skosmos/tree/issue805-alphabet-collation