These are historical forms of Germanic languages and would be useful for etymologies.

odt (Old Dutch)

• Wikidata item: https://www.wikidata.org/wiki/Q443089
• Existing lexemes: https://www.wikidata.org/wiki/Special:WhatLinksHere/Q443089?namespace=146
• ISO 639-3: https://iso639-3.sil.org/code/odt
• BCP 47: https://r12a.github.io/app-subtags/index?check=odt

ofs (Old Frisian)

• Wikidata item: https://www.wikidata.org/wiki/Q35133
• Existing lexemes: https://www.wikidata.org/wiki/Special:WhatLinksHere/Q35133?namespace=146
• ISO 639-3: https://iso639-3.sil.org/code/ofs
• BCP 47: https://r12a.github.io/app-subtags/index?check=ofs

osx (Old Saxon)

• Wikidata item: https://www.wikidata.org/wiki/Q35219
• Existing lexemes: https://www.wikidata.org/wiki/Special:WhatLinksHere/Q35219?namespace=146
• ISO 639-3: https://iso639-3.sil.org/code/osx
• BCP 47: https://r12a.github.io/app-subtags/index?check=osx

frk (Frankish)

• Wikidata item: https://www.wikidata.org/wiki/Q10860505
• Existing lexemes: https://www.wikidata.org/wiki/Special:WhatLinksHere/Q10860505?namespace=146
• ISO 639-3: https://iso639-3.sil.org/code/frk
• BCP 47: https://r12a.github.io/app-subtags/index?check=frk

Already done (as part of T341409):

dum (Middle Dutch)

• Wikidata item: https://www.wikidata.org/wiki/Q178806
• Existing lexemes: https://www.wikidata.org/wiki/Special:WhatLinksHere/Q178806?namespace=146
• ISO 639-3: https://iso639-3.sil.org/code/dum
• BCP 47: https://r12a.github.io/app-subtags/index?check=dum