chore(theme): add defaultLang

[cipchk]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ng-alain/delon/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[ ] No

Other information

[ng-alain-bot]

Preview is ready!

[codecov]

Codecov Report

Merging #1705 (48980af) into master (c0c731b) will decrease coverage by 0.08%.
The diff coverage is 18.18%.

❗ Current head 48980af differs from pull request most recent head c1fa65c. Consider uploading reports for the commit c1fa65c to get more accurate results

@@            Coverage Diff             @@
##           master    #1705      +/-   ##
==========================================
- Coverage   95.09%   95.01%   -0.08%     
==========================================
  Files         315      315              
  Lines        8882     8891       +9     
  Branches     1662     1665       +3     
==========================================
+ Hits         8446     8448       +2     
- Misses        365      372       +7     
  Partials       71       71              

Files	Coverage Δ
packages/theme/src/provide.ts	18.18% <18.18%> (+18.18%)	⬆️