Localisation with UI translations in as many languages as possible

[spwoodcock]

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

• FMTM is currently English only.

Describe the solution you'd like

• Localisation via Weblate: https://hosted.weblate.org/projects/hotosm/
• Translations could be shared with TM and other tools, if strings match.
• The community contributes, we download XLIFF or PO and commit to this repo, then placeholders in the frontend HTML are replaced depending on locale selection.

Describe alternatives you've considered

• Many other tools are closed source.

Additional context

• We need to decide on a tool to use for i18n in React.