LanguagesResource.getAllMessages throws IllegalStateException on duplicate language keys

Problem Statement

The back-end i18n messages endpoint (GET .../v2/languages/{lang}/messages, served by LanguagesResource.getAllMessages) throws a 500 / IllegalStateException: Duplicate key ... whenever the language keys for a locale contain two entries with the same key. This breaks the admin UI flow that loads all localized messages (e.g. opening the Site Browser portlet triggers the request).

Observed log:

WARN mapper.RuntimeExceptionMapper - Duplicate key com.dotcms.repackage.javax.portlet.title.c-Pages (attempted merging values Pages and Pages)
java.lang.IllegalStateException: Duplicate key com.dotcms.repackage.javax.portlet.title.c-Pages (attempted merging values Pages and Pages)
    at java.base/java.util.stream.Collectors.duplicateKeyException(Collectors.java:135)
    ...
    at com.dotcms.rest.api.v2.languages.LanguagesResource.getAllMessages(LanguagesResource.java:492)

Root cause: In LanguagesResource.getAllMessages, the language-keys branch (used when localization enhancements are disabled) collects with a strict Collectors.toMap that has no merge function:

// LanguagesResource.java ~L491-493
final Map<?,?> mapLanguageKeys = languageAPI
        .getLanguageKeys(currentLocale.getLanguage()).stream().collect(
                Collectors.toMap(LanguageKey::getKey, LanguageKey::getValue)); // ← throws on duplicate key

Collectors.toMap without a merge function throws on any duplicate key. Notably, the other two collectors in the very same method (the enhanced language-variables branch ~L482 and the legacy language-variables branch ~L501) already pass a merge function and only log a warning — this one branch is the outlier.

The duplicate data here is a portlet-title language key, com.dotcms.repackage.javax.portlet.title.c-Pages (both values Pages). These keys are written by PortletAPIImpl.savePortlet (com.dotcms.repackage.javax.portlet.title.<portletId>) across all languages, so re-saving a custom content portlet can leave duplicate rows in the language_key table, which then makes this endpoint fail.

Context: Found while QA-testing #34435 (Portlet cache / Redis fix). It is unrelated to that fix — different subsystem (i18n messages REST endpoint), different root cause (missing merge function + duplicate language_key rows). Filed separately per that investigation.

Steps to Reproduce

1. Have (or create) a custom content portlet whose title language key com.dotcms.repackage.javax.portlet.title.<portletId> exists more than once in the language_key table for a locale — e.g. a custom portlet "Pages" (c-Pages). This can occur after saving/re-saving a custom portlet.
2. Log into the back-end and open a portlet (e.g. Site Browser), which makes the admin UI request all i18n messages (LanguagesResource.getAllMessages).
3. Observed: the request returns 500 and the server logs IllegalStateException: Duplicate key com.dotcms.repackage.javax.portlet.title.c-Pages.
4. Expected: the endpoint returns the full message map, deterministically resolving the duplicate (as the sibling collectors in the same method already do).

Acceptance Criteria

• LanguagesResource.getAllMessages no longer throws when the language keys for a locale contain duplicate keys; it resolves them deterministically with a merge function, consistent with the two sibling collectors in the same method.
• A duplicate key is logged at warn (matching the existing branches) instead of aborting the whole response with a 500.
• Investigate the source of the duplicate portlet-title language_key rows created via PortletAPIImpl.savePortlet (com.dotcms.repackage.javax.portlet.title.<portletId>); either prevent duplicate insertion on re-save or document why duplicates are expected.
• Regression coverage: getAllMessages returns 200 with the full message set when duplicate keys are present.

dotCMS Version

Current Evergreen 26.07.13-1

Severity

Medium - Some functionality impacted

Links

• Related (context only, not a duplicate): #34435 (Portlet cache Redis fix — this was surfaced while testing it)
• Freshdesk ticket of the related issue: https://helpdesk.dotcms.com/a/tickets/34992

Start in LanguagesResource.getAllMessages around the language-keys collector near line 492, compare it with the two sibling collectors that already log duplicate keys, and trace duplicate portlet-title rows through PortletAPIImpl.savePortlet. Verify that duplicate keys produce a warning and a successful full message response, then investigate whether re-saving should prevent duplicate insertion or document why duplicates are expected.