I believe that they are already somewhere in the FPC RTL, but just in case, here is the h2pas conversion. Not much work, took less than 0.1 second. Know your tools
No need for h2pas options.
Note that there is a define per code page, so you should map those XK_<xxx> defines to the language families you want or set the define manually. Easy.
One remark more: the copyright is last changed in 1998 and there have been many, many additions after that, especially for unicode.
I suspect that keysymdef.h is an old version, but it will still work for the things that ARE included.. (e.g. smilies are not included)
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The key mappings are in ./rtl/charmaps, ./rtl/ucmaps and ./rtl/objpas in the fpc source directory rtl root. It may be that additionally the Lazarus LCL has specific mappings for UTF8, since the rtl does not directly support UTF8 (But it does support UTF16)