Pin the buy e2e locale so the collection-IBAN test stops depending on account data

[joshuakrueger-dfx]

What

e2e/buy-process.spec.ts → the should toggle between the personal and the collection IBAN test now opens the buy screen with &lang=en.

Why

The test asserts English labels (Payment Information, Show collection IBAN), but without a lang parameter the UI locale is resolved as

lang (URL) ?? user.language ?? storedLanguage ?? browserLanguage

(src/contexts/settings.context.tsx). With no parameter the locale therefore comes from the test account's stored user.language — server-side data anyone can change. It is currently German, so the app renders Zahlungsinformation, the English selectors match nothing and the test fails with element(s) not found.

Evidence

Run against an unmodified checkout of the current develop (51ce782), repo-pinned Playwright 1.57.0:

	Result
without lang=en	1 failed — element(s) not found
with lang=en	1 passed

The baseline screenshots are unchanged by this PR — the parameter changes the locale, not the rendering that the baselines capture.

Scope

Test-only, four lines (three of them the comment explaining the failure mode). No production code, no other test touched.

Necessity

Symptom (verbatim): Error: expect(locator).toBeVisible() failed — Locator: getByRole('heading', { name: 'Payment Information' }).locator('..').getByRole('button', { name: 'Show collection IBAN' }) — Error: element(s) not found. Reproduced on an unmodified checkout of develop 51ce782, so it is not caused by any code change.

Scale: this test is the only visual guard for the collection-IBAN UI, and it fails for every developer whose test account language is not English. The account language changed after the test was written on 2026-08-04, and two people hit it on that same day. It also blocks validating the two regenerated baselines in #1270.

Smaller fix considered: setting the test account language back to English on the dev API, zero lines of code — insufficient because that is mutable server-side state which the next person can change back, which is exactly how the test broke in the first place.

[joshuakrueger-dfx]

@marassteiner please review

[marassteiner]

EN: Working on this now — job dfxswiss__services__1269__pr-review.
DE: Ich arbeite jetzt daran — Auftrag dfxswiss__services__1269__pr-review.

[marassteiner]

Review summary

Recommendation: approve

No merge-blockers. Test-only change; production code untouched. CI is green (Build and test, Analyze, CodeQL, review).

What changed

e2e/buy-process.spec.ts — collection-IBAN toggle test now opens the buy URL with &lang=en, so English role selectors (Payment Information, Show collection IBAN) no longer depend on mutable server-side user.language.

Gate A — diff review (conformity + logic)

Both independent review lanes completed a full pass over the PR diff vs develop and reported 0 findings.

• Locale priority in settings.context.tsx is lang (URL) → user.language → store → browser; pinning lang=en correctly overrides account language.
• Matches existing e2e convention (support-issue-receiver-iban.spec.ts, payment-and-special.spec.ts).
• Scope matches the PR claim; comment documents the failure mode; no type-safety / security / semantic merge issues.

Gate B — local software run

Step	Result
npm ci	Failed on review host with npm 11 / Node 24 (package.json vs lock out of sync for optional platform packages). Not attributable to this PR (diff does not touch lockfile/deps).
npm install	OK (fallback per review procedure)
npm run lint	OK (exit 0)
CI=true npm run test -- --watchAll=false	72 suites / 788 tests passed
npm run start:dev (PORT=3019)	Compiled (No issues found.); process listens on *:3019; GET http://127.0.0.1:3019/ → HTTP 200

Merge-blockers

None.

Follow-up findings

None filed. (A pre-existing sibling test in the same file also uses English labels without lang=en; it is outside this PR’s claim and not introduced or worsened here.)

CI

All PR checks green at review time: Build and test, Analyze, CodeQL, review.

No merge from this review.