TextInfo.ToTitleCase mishandles Dutch IJ digraph on neutral nl culture

[rjgotten]

Description

TextInfo.ToTitleCase mishandles the Dutch IJ digraph with the neutral nl culture.
It only works correctly with specific cultures.

Reproduction Steps

CultureInfo.GetCultureInfo("nl-NL").TextInfo.ToTitleCase("de ijsvogel")
// ✅ "De IJsvogel"
CultureInfo.GetCultureInfo("nl").TextInfo.ToTitleCase("de ijsvogel")
// ⛔ "De Ijsvogel"

Expected behavior

The neutral Dutch culture should capitalize the ij digraph.

Actual behavior

The neutral Dutch culture does not capitalize the ij digraph.

Regression?

No response

Known Workarounds

Only use TextInfo.ToTitleCase with a specific Dutch culture.

Configuration

.NET runtime: v10.0.11

Other information

Source-verifiable cause: TextInfo.ToTitleCase uses a .StartsWith("nl-") check on the TextInfo instance's culture name. That naturally fails for the neutral Dutch culture.

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