DF-1226: Add Welsh language translations to the clientside maps

[davidjamesstone]

Proposed change

Maps plugin: Add Welsh translation capability

Jira ticket: https://eaflood.atlassian.net/browse/DF-1226

Type of change

• Bug fix
• New feature
• Breaking change
• Misc. (documentation, build updates, etc)

Checklist

• You have executed this code locally and it performs as expected.
• You have added tests to verify your code works.
• You have added code comments and JSDoc, where appropriate.
• There is no commented-out code.
• You have added developer docs in README.md and docs/* (where appropriate, e.g. new features).
• The tests are passing (npm run test).
• The linting checks are passing (npm run lint).
• The code has been formatted (npm run format).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
1 Accepted issue

Measures
0 Security Hotspots
90.6% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[jbarnsley10]

Just a general point about passing an optional 'lang' param ... my preference would be to have the 'lang' required in all cases apart from the top level call (where it might default to en-GB say). That way you can be sure you've not forgotten to pass a 'lang' into an inner method i.e. the linter would pick that up.
But if you have sufficient test coverage, it should be fine.

[davidjamesstone]

I kept this in because this function is also used by forms-designer (to generate the "map review" page) and it doesn't have a language switch. I could make it mandatory but we'd have to then pass in en-GB from designer

[jbarnsley10]

Good work. Just my observation about the optional 'lang' param but I'll leave that up to you to decide what you think is best.