Re-translate displayed survey on language change

Summary

The Android SDK resolves a survey's display language once, at show time. A displayed survey is frozen after that: changing the language person property doesn't re-translate it, and there's no delegate hook to update a rendered survey in place.

Current State

• showSurvey() in posthog-android/src/main/java/com/posthog/android/surveys/PostHogSurveysIntegration.kt resolves the language (overrideDisplayLanguage → person property language → device locale) and the translations into locals, then hands the delegate a one-shot PostHogDisplaySurvey. $survey_language is stamped from that snapshot.
• PostHogSurveysDelegate (posthog/src/main/java/com/posthog/surveys/PostHogSurveysDelegate.kt) only exposes renderSurvey and cleanupSurveys, so there's no way to push new content to a survey that's already rendered.
• setPersonPropertiesForFlags() only triggers a flags reload, and that path doesn't reprocess surveys. canShowNextSurvey() bails while a survey is active, so nothing ever revisits the one on screen.

Expected Behavior

When person properties change while a survey is displayed and the resolved language differs from what's shown, the SDK should re-resolve the active survey's translation and push it to the delegate for an in-place update. $survey_language on subsequent survey events should match what's actually on screen.

Concretely this needs an optional updateSurvey on PostHogSurveysDelegate (implemented by the Compose delegate) plus a person-properties-changed subscription in PostHogSurveysIntegration.

Reference Implementation

posthog-ios: https://github.com/PostHog/posthog-ios/pull/686 adds an optional updateSurvey to the surveys delegate and a person-properties-for-flags change subscription, and no-ops when the matched language is unchanged.

Related

• posthog-js (browser): https://github.com/PostHog/posthog-js/issues/4174
• posthog-js (React Native): https://github.com/PostHog/posthog-js/issues/4175
• posthog-flutter: https://github.com/PostHog/posthog-flutter/issues/483

Start by reading showSurvey() in posthog-android/src/main/java/com/posthog/android/surveys/PostHogSurveysIntegration.kt and the delegate contract in posthog/src/main/java/com/posthog/surveys/PostHogSurveysDelegate.kt. Use the posthog-ios pull request as a reference, then inspect the Compose delegate and person-properties-for-flags flow. Done means an active survey updates in place when the resolved language changes, while unchanged languages are ignored and later events report the displayed language.