Add internationalisation to applications

[mattdy]

Area

Web UI

Problem / Motivation

Add ability for frontend applications to be displayed in different languages

Proposed Solution

• Implement some sort of crowdsourced translation service
• Provide language template file that sits across all frontend applications
• Allow either per-user or per-installation configuration of language

Additional Context

No response

[mattdy]

Potentially blocked by #364 if we want to store this on a per-user basis.

Best practice may be to have a global default language as a server setting, then allow per-user customisation.