diff --git a/src/components/TranslationModal.vue b/src/components/TranslationModal.vue
index 24df5cc95a..f1e87633a4 100644
--- a/src/components/TranslationModal.vue
+++ b/src/components/TranslationModal.vue
@@ -92,6 +92,26 @@ import logger from '../logger.js'
 import { translateText } from '../service/translationService.js'
 import useMainStore from '../store/mainStore.js'
 
+const normalize = (code) => code?.toLowerCase().replace(/_/g, '-')
+const primarySubtag = (code) => normalize(code)?.split('-')[0]
+
+/**
+ * Find the option closest to a language code.
+ *
+ * The interface reports `pt-BR` while providers list `pt_BR`, and either side
+ * may omit the region the other one has, so neither separators nor regions can
+ * be compared verbatim.
+ *
+ * @param {Array} languages options offered by the provider
+ * @param {string|null} code language code to look for
+ * @return {object|null} the matching option, or null when the provider has none
+ */
+function findLanguage(languages, code) {
+	return languages.find((language) => normalize(language.value) === normalize(code))
+		?? languages.find((language) => primarySubtag(language.value) === primarySubtag(code))
+		?? null
+}
+
 export default {
 	name: 'TranslationModal',
 
@@ -152,7 +172,7 @@ export default {
 	},
 
 	async mounted() {
-		this.selectedTo = this.availableOutputLanguages.find((language) => language.value === this.userLanguage) || null
+		this.selectedTo = findLanguage(this.availableOutputLanguages, this.userLanguage)
 		this.selectedFrom = this.availableInputLanguages.find((language) => language.value === 'detect_language')
 		this.$nextTick(() => {
 			// FIXME trick to avoid focusTrap() from activating on NcSelect
diff --git a/src/tests/unit/components/TranslationModal.vue.spec.js b/src/tests/unit/components/TranslationModal.vue.spec.js
new file mode 100644
index 0000000000..73a07456ae
--- /dev/null
+++ b/src/tests/unit/components/TranslationModal.vue.spec.js
@@ -0,0 +1,113 @@
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+import { createLocalVue, shallowMount } from '@vue/test-utils'
+import { createPinia, setActivePinia } from 'pinia'
+import TranslationModal from '../../../components/TranslationModal.vue'
+import Nextcloud from '../../../mixins/Nextcloud.js'
+import useMainStore from '../../../store/mainStore.js'
+
+const { getLanguage } = vi.hoisted(() => ({ getLanguage: vi.fn() }))
+
+vi.mock('@nextcloud/l10n', async () => ({
+	...await vi.importActual('@nextcloud/l10n'),
+	getLanguage,
+}))
+
+const localVue = createLocalVue()
+
+localVue.mixin(Nextcloud)
+
+describe('TranslationModal', () => {
+	const language = (value) => ({ id: value, value, name: value })
+
+	const mountModal = ({ input = [], output = [], detectedForeignLanguage = null } = {}) => {
+		const store = useMainStore()
+		store.translationInputLanguages = input.map(language)
+		store.translationOutputLanguages = output.map(language)
+
+		return shallowMount(TranslationModal, {
+			propsData: {
+				message: 'Bonjour tout le monde',
+				richParameters: {},
+				detectedForeignLanguage,
+			},
+			localVue,
+		})
+	}
+
+	beforeEach(() => {
+		setActivePinia(createPinia())
+		getLanguage.mockReturnValue('en')
+	})
+
+	describe('target language', () => {
+		it('picks the interface language', () => {
+			getLanguage.mockReturnValue('de')
+
+			const view = mountModal({ output: ['en', 'de'] })
+
+			expect(view.vm.selectedTo?.value).toBe('de')
+		})
+
+		it('matches the interface hyphen against the provider underscore', () => {
+			getLanguage.mockReturnValue('pt-BR')
+
+			const view = mountModal({ output: ['pt_PT', 'pt_BR'] })
+
+			expect(view.vm.selectedTo?.value).toBe('pt_BR')
+		})
+
+		it('settles for the primary language when the provider offers no regional variant', () => {
+			getLanguage.mockReturnValue('pt_BR')
+
+			const view = mountModal({ output: ['en', 'pt'] })
+
+			expect(view.vm.selectedTo?.value).toBe('pt')
+		})
+
+		it('prefers the exact match over the primary language', () => {
+			getLanguage.mockReturnValue('pt-BR')
+
+			const view = mountModal({ output: ['pt', 'pt_BR'] })
+
+			expect(view.vm.selectedTo?.value).toBe('pt_BR')
+		})
+
+		it('selects nothing when the provider does not offer the language at all', () => {
+			getLanguage.mockReturnValue('de')
+
+			const view = mountModal({ output: ['en', 'fr'] })
+
+			expect(view.vm.selectedTo).toBeNull()
+		})
+	})
+
+	describe('source language', () => {
+		it('lets the provider detect the language when it can', () => {
+			const view = mountModal({ input: ['detect_language', 'fr'], detectedForeignLanguage: 'fr' })
+
+			expect(view.vm.selectedFrom?.value).toBe('detect_language')
+		})
+
+		it('falls back to the detected language', () => {
+			const view = mountModal({ input: ['en', 'fr'], detectedForeignLanguage: 'fr' })
+
+			expect(view.vm.selectedFrom?.value).toBe('fr')
+		})
+
+		it('matches a regional variant of the detected language', () => {
+			const view = mountModal({ input: ['en', 'pt_BR'], detectedForeignLanguage: 'pt' })
+
+			expect(view.vm.selectedFrom?.value).toBe('pt_BR')
+		})
+
+		it('selects nothing when there is no detected language', () => {
+			const view = mountModal({ input: ['en', 'fr'] })
+
+			expect(view.vm.selectedFrom).toBeNull()
+		})
+	})
+})