Fixes purchase intent does not work if Brave is set to JP locale - 1.12.x

[tmancey]

Uplift of #6076
Resolves brave/brave-browser#10737

• You have checked CI and the builds, lint, and tests all pass or are not related to your PR.
• You have tested your change on Nightly.
• The PR milestones match the branch they are landing to.

After you merge:

• The associated issue milestone is set to the smallest version that the changes is landed on.

[moritzhaller]

LGTM!

[kjozwiak]

test-browser failed on Linux as per https://ci.brave.com/job/pr-brave-browser-issues-10737-1.12.x/1/execution/node/459/log/. However, this is a known intermittent issue and not due to this specific PR.

20:44:32  1 test failed:
20:44:32      RewardsBrowserTest.NotVerifiedWallet (../../brave/components/brave_rewards/browser/test/rewards_browsertest.cc:241)

test-install failed on macOS as per https://ci.brave.com/job/pr-brave-browser-issues-10737-1.12.x/1/execution/node/583/log/. However, this is a known intermittent issue as well.

[kjozwiak]

Uplift into 1.12.x approved after deliberating with @brave/uplift-approvers. We basically ran out of time to QA this on Nightly before we uplift. However, @moritzhaller mentioned this was tested and is working as expected. QA will verify on the 1.11.x RC3.