Umlauts grouped in summary (U and Ü, A and Ä etc) I faced the problem with summary attachment which includes umlauts like: U and Ü, A and Ä; O and Ö etc. For example if two nodes starting with letters U and Ü

Umlauts 
Ümlauts


only U letter will be displayed in summary. In case when some of nodes starting only with Ü, this letter Ü in correctly displayed in summary, problem appears when nodes have both U and Ü as capital letters.



Later I figured out that it's caused by GROUP BY query part

SELECT SUBSTRING(node.title, 1, 1) AS title_truncated, COUNT(node.nid) AS num_records
FROM node node
GROUP BY title_truncated
ORDER BY title_truncated ASC


Nodes with first U and Ü letters are treated were treated as U. How can I manage this problem?
If I had to take a guess at this it would be that your database is using utf8 and the default collation of utf8_general_ci. If I understand correctly, this collation does not handle diacritics very well, and would consider U and Ü the same. You may have better luck with utf8_unicode_ci. That said, most of my Unicode experience is with Elasticsearch, so I know less about MySQL collation (assuming that is your database). You may have more luck running this by a database-specific stackexchange.

Here is a reference on the two collation types: https://stackoverflow.com/questions/1036454/what-are-the-diffrences-between-utf8-general-ci-and-utf8-unicode-ci.