It is (sometimes) one letter culturally speaking and in lettering. A Dutch alphabet as taught to children used to end in 'X IJ Z' instead of 'X Y Z', although this is no longer the case ever since people started eating 'yoghurt' in the twentieth century. In capitalisation of words too it is treated as a single 'letter' (e.g., 'IJsselmeer' for the lake; note the uppercase 'J').

If you dig deeper on the Unicode website you'll find that the reason those codepoints are included is compatibility with 'certain very rare legacy (non-Unicode) character encodings'. They are not 'deprecated' as compatibility characters for those old legacy encodings, but 'deprecated' as suitable for rendering Dutch text unencumbered by those early code pages.

Words have meanings. "deprecated" has a very specific meaning in Unicode and it does not apply to this code point. A lot of characters we use on a daily are marked <compat>.

This is not a codepoint in daily use. It never was outside of those few legacy encodings. If it is not deprecated, it is not so because it never was in common use in the first place. The concept of the ij/IJ as a single codepoint is deprecated, regardless of the technical classification in Unicode.

If you are claiming that 0x0132 is a codepoint in common use or required for correctly spelled Dutch, you are mistaken.

> If you are claiming that 0x0132 is a codepoint in common use or required for correctly spelled Dutch, you are mistaken.

I made no comment in support or opposition of that. I cannot talk to that as I’m not familiar with either Dutch or that letter. However there are many compat characters in Unicode and there are incredibly few deprecated ones so I was addressing the deprecation claim (and what I believe is a misuse of the term letter). You’re interpreting things into my replies that just aren’t there.

Compat characters are very useful and even if they are not stored all the time, they often show up in text processing in memory for better glyph selection.