Handle invalid issues (#18111)

* Handle invalid issues

- When you hover over a issue reference, and the issue doesn't exist, it
will just hang on the loading animation.
- This patch fixes that by showing them the pop-up with a "Error
occured" message.

* Add I18N

* refactor

* fix comment for lint

* fix unit test for i18n

* fix unit test for i18n

* add comments

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

integrations/api_releases_test.go

@@ -207,7 +207,7 @@ func TestAPIGetReleaseByTag(t *testing.T) {
 
 	var err *api.APIError
 	DecodeJSON(t, resp, &err)
-	assert.EqualValues(t, "Not Found", err.Message)
+	assert.NotEmpty(t, err.Message)
 }
 
 func TestAPIDeleteReleaseByTagName(t *testing.T) {

integrations/repo_branch_test.go

@@ -141,7 +141,7 @@ func TestCreateBranchInvalidCSRF(t *testing.T) {
 	resp = session.MakeRequest(t, NewRequest(t, "GET", loc), http.StatusOK)
 	htmlDoc := NewHTMLParser(t, resp.Body)
 	assert.Equal(t,
-		"Bad Request: Invalid CSRF token",
+		"Bad Request: invalid CSRF token",
 		strings.TrimSpace(htmlDoc.doc.Find(".ui.message").Text()),
 	)
 }