feat: Setting default language to english in APISIX Dashboard

[dileepajayakody]

Please answer these questions before submitting a pull request, or your PR will get closed.

Why submit this pull request?

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What changes will this PR take into?

This PR sets the default language in apisix-dashboard to en-US.

Related issues

Checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[codecov-commenter]

Codecov Report

Merging #2212 (a87f457) into master (ad7e3e7) will increase coverage by 2.97%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2212      +/-   ##
==========================================
+ Coverage   65.16%   68.13%   +2.97%     
==========================================
  Files         184      127      -57     
  Lines        7257     3352    -3905     
  Branches      824      824              
==========================================
- Hits         4729     2284    -2445     
+ Misses       2244     1068    -1176     
+ Partials      284        0     -284     

Flag	Coverage Δ
backend-e2e-test	?
backend-unit-test	?
frontend-e2e-test	68.13% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
api/internal/core/storage/etcd.go
api/internal/handler/data_loader/route_export.go
...pi/internal/handler/plugin_config/plugin_config.go
api/internal/utils/consts/api_error.go
api/internal/core/store/storehub.go
api/internal/handler/schema/schema.go
api/internal/filter/authentication.go
api/internal/handler/healthz/healthz.go
api/internal/core/migrate/dataset.go
api/internal/core/store/store.go
... and 47 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ad7e3e7...a87f457. Read the comment docs.

[bzp2010]

LGTM