Allow multilingual fields

[tosteiner]

Is your feature request related to a problem? Please describe.

One of the presses seeking to use Thoth, L'Harmattan Open Access, has publications in a variety of European languages (incl. Hungarian, English, Slovakian, etc.). Their existing metadata catalogue includes records that also store metadata in multiple languages (e.g. Hungarian- next to English-language metadata sets for a book published in Hungarian)

Describe the solution you'd like
Extend Thoth's data model to enable the recording of parallel versions of metadata in x number of languages.

Additional context
Also relevant to other presses and our collaboration with PKP - Alec Smecher noted that OMP encourages the use e.g. of multilingual titles, abstracts, etc.

Partial links to

a) #96
b) Recommendation 61 of the Scoping Report, and preceding paragraph noting

There is also a requirement to look at linguistic diversity and metadata. The English language (unsurprisingly) dominates. Many software packages assume English is the first language both as language of the software interface, and as input language. However, many OA monograph publishers exist to publish in other languages. OPERAS is looking into translation software and this could be extended to metadata . However, there may be problems with characters outside the standard Latin character set, as well as RTL scripts (Hebrew, Arabic), TTB scripts (Mongolian), context-sensitive scripts (Arabic), and abigudas (most South Asian scripts, Ethiopian, Inuit). Source

[ja573]

So far we've identified title and abstracts – we need to clarify wether other fields would need multilingualism

[ja573]

related #435