gui, man, authors: Update docs, translations, and contributors

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gui/default/assets/lang/lang-bg.json

gui/default/assets/lang/lang-ca@valencia.json

gui/default/assets/lang/lang-cs.json

gui/default/assets/lang/lang-da.json

gui/default/assets/lang/lang-de.json

gui/default/assets/lang/lang-el.json

gui/default/assets/lang/lang-en-AU.json

gui/default/assets/lang/lang-en-GB.json

gui/default/assets/lang/lang-eo.json

gui/default/assets/lang/lang-es-ES.json

gui/default/assets/lang/lang-es.json

gui/default/assets/lang/lang-eu.json

gui/default/assets/lang/lang-fi.json

gui/default/assets/lang/lang-fr.json

gui/default/assets/lang/lang-fy.json

gui/default/assets/lang/lang-hu.json

gui/default/assets/lang/lang-id.json

gui/default/assets/lang/lang-it.json

gui/default/assets/lang/lang-ja.json