Adding Sprint Health Gadget / Days Remaining in Sprint Gadget does not work when user language setting is not English

Summary

Adding the Sprint Health Gadget or Days Remaining in Sprint Gadget will not work correctly when selecting the Auto sprint option when the user's preferred language is not English.

Environment

• JIRA Cloud v1000.383.2 (I don't have a permission to add new Affects Version/s that's why I wrote here.)
• JIRA Server 7.2.2

Steps to Reproduce

1. Create a board
2. Create a sprint
3. Add an issue to the backlog
4. Start the sprint
5. Change user language to Japanese (Confirmed this happens in Spanish, Korean, and Chinese as well, but possibly all other languages)
6. Add Sprint Health Gadget ("スプリントヘルスガジェット" in Japanese) or Days Remaining in Sprint Gadget ("スプリントガジェット内の残り日数" in Japanese) to a dashboard
7. Set sprint as Next Sprint Due (auto) ("次のスプリント期限（自動）" in Japanese) in the configuration
8. Press "Save" button

Expected Results

The gadget should display the sprint health info correctly.

Actual Results

An error "リクエストしたボードを表示できません。ボードが存在しないかまたは表示する権限がありません。" was shown. ("The requested board cannot be viewed because it either does not exist or you do not have permission to view it." in English.)

Just changing the user language back to English didn't solve the problem.

Notes

• This problem never occurred on JIRA 6.4.x
• This problem never occurred on Sprint Burndown Gadget
• Investigation
  When pressing the "Save" button, I can find the following accesses in developer tool.
  When it comes to the one in Japanese setting, sprintId seems to be corrupted.
  • Pressing the "Save" button in Japanese setting
    • https://xxxxx.atlassian.net/rest/greenhopper/1.0/gadgets/sprints/health?rapidViewId=7&sprintId=%26%2333258%3B%26%2321205%3B&_=1475197516579
  • Pressing the "Save" button in English setting
    • https://xxxxx.atlassian.net/rest/greenhopper/1.0/gadgets/sprints/health?rapidViewId=7&sprintId=15&_=1475197064445

Workaround

1. Change the user language back to English
2. Edit the gadget on the dashboard and save it. (This should immediately show the data once more on the gadget)
3. Change the user language back to their preferred language once again