Fix grammatical error
Merge pull request #6429 from PendalF89/patch-1

[skip ci] Fix grammatical error
docs/guide-ja/README.md - updated [ci skip]
docs/guide-ja/db-migrations.md - started translation [ci skip]
docs/guide-ja/db-migrations.md - completed [ci skip]
Merge pull request #6433 from softark/docs-guide-ja-db-migrations

/docs/guide-ja/db-migrations.md added [ci skip]
Fixes #6404: advanced application template `Alert` widget was generating duplicate IDs in case of multiple flashes
Fixes #6372. [skip ci]