bug#24603: [PATCHv5 08/11] Implement rules for title-casing Dutch ij ‘letter’ (bug#24603)

[Eli Zaretskii <eliz@gnu.org>]

> From: Michal Nazarewicz <mina86@mina86.com>
> Date: Thu,  9 Mar 2017 22:51:47 +0100
> 
> +    /* In Dutch, ‘ij’ is a digraph and when capitalised the whole thing is upper
> +       cased.  Unicode has ‘ij’ and ‘IJ’ (with proper casing mappings) but they
> +       aren’t always used so we cannot/should not rely on them.
> +
> +       Note that rule for capitalising ‘ij’ as a single letter is not present in
> +       Unicode 9.0’s SpecialCasing.txt.  On the flip side, Firefox implements
> +       this as well so we’re not completely alone.

If this is not mandated by Unicode 9.0 (and not by the latest draft of
10.0, AFAICS), shouldn't we have a user option for this, by default
off?

> +       There are words where ‘ij’ are two separate letters (such as bijectie or
> +       bijoux) in which case the capitalisation rules do not apply.  I (mina86)
> +       have googled this a little and couldn’t find a Dutch word which beings
> +       with ‘ij’ that is not a digraph so we should be in the clear since we
> +       only care about the initial. */

I'm not sure I get this right: does this mean that writing in English
(or any other non-Dutch language) in a Dutch locale will automatically
capitalize "ij" to "IJ", just because the default value of
buffer-language is "nl_NL" or somesuch, and no specific language was
set for the buffer?  Wouldn't that surprise users?