Title: Case-insensitive search issue with Turkish characters (İ / i)

[96273]

I would like to report a possible issue with the search functionality in SumatraPDF.

While searching within a PDF document, I noticed that case-insensitive search does not seem to work correctly for certain non-ASCII characters, specifically Turkish letters.

Description of the issue

In the document below, there is a word: "İbradı" (capital dotted "İ").

When I search for "ibradı" (all lowercase), the word is not found.
When I search for "İbradı" (with uppercase "İ"), it is found immediately.

This suggests that the search may not be properly handling Unicode case folding for Turkish characters.

Steps to reproduce

Open the following PDF:
https://cdniys.tarimorman.gov.tr/api/File/GetFile/330/Sayfa/1416/1778/DosyaGaleri/21._orman_kaynaklarindan_faydalanma.pdf

Search for: ibradı — No results

Search for: İbradı — Result found

Expected behavior

The search should ideally be case-insensitive (unless explicitly set otherwise) and correctly handle Unicode characters such as Turkish dotted/dotless "i".

Actual behavior

Search appears to be case-sensitive or not fully Unicode-aware for this character.

Additional materials

Screenshot:

Image

I am not sure whether this is an intended limitation or a bug, but I wanted to report it in case it can be improved.

Thank you for your work on SumatraPDF!

[GitHubRulesOK]

there is "Rarely" any such thing as Unicode in most PDF as the letters are entirely numeric tokens like 10010101 and those are then added as single or double bytes for look-up into other numeric entries that are then displayed as if a local encoding from say a Turkish font so the search may be 404 or 101 or any thing for a capital and its lower case certainly even English may not be 2 sets of 26 sequential numbered tokens.
so the one and only brad is not pitt but this one İbradı