* config/lang.hb
* utils/hbmk2/hbmk2.hbp
* contrib/hbrun/doc/hbrun.es_ES.md -> contrib/hbrun/doc/hbrun.es.md
* utils/hbmk2/doc/hbmk2.es_ES.md -> utils/hbmk2/doc/hbmk2.es.md
* utils/hbmk2/po/hbmk2.es_ES.po -> utils/hbmk2/po/hbmk2.es.po
* 'es_ES' -> 'es'
; General rule is to support the "root" language and any number
of additional dialects, f.e. 'es'+'es_419', 'pt'+'pt_BR', 'fr').
(as opposed to dialects only, f.e. 'es_ES'+'es_419', 'pt_PT'+'pt_BR', 'fr_FR')
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