SharePoint 2013 REST API odata $filter ignores uni

Question

I'm trying to use SharePoint 2013 REST API (odata) with unicode characters such as umlauts (ä ö ü).

...?$select=Title%2CID&$filter=substringof%28%27hello%20w%F6rld%27%2C%20Title%29&$orderby=ID%20desc&$top=14

^^ should search for "hello w*ö*rld" using substringof('...', Field)

I'm escaping the URL correctly (and also single quotes with double quotes) and filtering works for all kinds of characters (even backslash and quotes), however, entering ä/ö/ü or any other unicode character has no effect, it is as if those characters were simply filtered out on the server side (i can insert a lot of ääääääs without changing the results).

Any idea how to escape those? I tried the obvious (%ab { \u1234 \xab x1234) without success. Can't find anything on the web or in the specs either.

Thanks for suggestions.

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UPDATE - SOLVED

I found that you can use the %uhhhh variant of escaping them:

?$filter=substringof('hello w%u00f6rld') 

Of course one must only escape that once (i.e. not the whole thing again), but it seems that's the way to go.

(can't answer my own question now lol)