diff --git a/packages/client/src/components/MkNote.vue b/packages/client/src/components/MkNote.vue
index f29b19e3cc..672939f9d9 100644
--- a/packages/client/src/components/MkNote.vue
+++ b/packages/client/src/components/MkNote.vue
@@ -81,6 +81,7 @@
 					:text="getNoteSummary(appearNote.reply)"
 					:plain="true"
 					:nowrap="true"
+					:lang="appearNote.reply.lang"
 					:custom-emojis="note.emojis"
 				/>
 			</div>
@@ -127,6 +128,7 @@
 								:text="translation.text"
 								:author="appearNote.user"
 								:i="$i"
+								:lang="targetLang"
 								:custom-emojis="appearNote.emojis"
 							/>
 						</div>
@@ -370,15 +372,12 @@ const enableEmojiReactions = defaultStore.state.enableEmojiReactions;
 const expandOnNoteClick = defaultStore.state.expandOnNoteClick;
 const lang = localStorage.getItem("lang");
 const translateLang = localStorage.getItem("translateLang");
+const targetLang = (translateLang || lang || navigator.language)?.slice(0, 2);
 
 const isForeignLanguage: boolean =
 	defaultStore.state.detectPostLanguage &&
 	appearNote.value.text != null &&
 	(() => {
-		const targetLang = (translateLang || lang || navigator.language)?.slice(
-			0,
-			2,
-		);
 		const postLang = detectLanguage(appearNote.value.text);
 		return postLang !== "" && postLang !== targetLang;
 	})();
diff --git a/packages/client/src/components/MkNotePreview.vue b/packages/client/src/components/MkNotePreview.vue
index 62bcc0f0c5..9782778e19 100644
--- a/packages/client/src/components/MkNotePreview.vue
+++ b/packages/client/src/components/MkNotePreview.vue
@@ -9,6 +9,7 @@
 				<div class="content">
 					<Mfm
 						:text="preprocess(text).trim()"
+						:lang="lang"
 						:author="$i"
 						:i="$i"
 						advanced-mfm
@@ -24,6 +25,7 @@ import preprocess from "@/scripts/preprocess";
 
 defineProps<{
 	text: string;
+	lang?: string;
 }>();
 </script>
 
diff --git a/packages/client/src/components/MkNoteSub.vue b/packages/client/src/components/MkNoteSub.vue
index 194a72d4b1..2e5b594a62 100644
--- a/packages/client/src/components/MkNoteSub.vue
+++ b/packages/client/src/components/MkNoteSub.vue
@@ -51,6 +51,7 @@
 								:text="translation.text"
 								:author="appearNote.user"
 								:i="$i"
+								:lang="targetLang"
 								:custom-emojis="appearNote.emojis"
 							/>
 						</div>
@@ -287,15 +288,12 @@ const enableEmojiReactions = defaultStore.state.enableEmojiReactions;
 const expandOnNoteClick = defaultStore.state.expandOnNoteClick;
 const lang = localStorage.getItem("lang");
 const translateLang = localStorage.getItem("translateLang");
+const targetLang = (translateLang || lang || navigator.language)?.slice(0, 2);
 
 const isForeignLanguage: boolean =
 	defaultStore.state.detectPostLanguage &&
 	appearNote.value.text != null &&
 	(() => {
-		const targetLang = (translateLang || lang || navigator.language)?.slice(
-			0,
-			2,
-		);
 		const postLang = detectLanguage(appearNote.value.text);
 		return postLang !== "" && postLang !== targetLang;
 	})();
diff --git a/packages/client/src/components/MkNotification.vue b/packages/client/src/components/MkNotification.vue
index 4c31793a36..7ea46b5a57 100644
--- a/packages/client/src/components/MkNotification.vue
+++ b/packages/client/src/components/MkNotification.vue
@@ -118,6 +118,7 @@
 					:text="getNoteSummary(notification.note)"
 					:plain="true"
 					:nowrap="!full"
+					:lang="notification.note.lang"
 					:custom-emojis="notification.note.emojis"
 				/>
 			</MkA>
@@ -131,6 +132,7 @@
 					:text="getNoteSummary(notification.note.renote)"
 					:plain="true"
 					:nowrap="!full"
+					:lang="notification.note.lang"
 					:custom-emojis="notification.note.renote.emojis"
 				/>
 			</MkA>
@@ -144,6 +146,7 @@
 					:text="getNoteSummary(notification.note)"
 					:plain="true"
 					:nowrap="!full"
+					:lang="notification.note.lang"
 					:custom-emojis="notification.note.emojis"
 				/>
 			</MkA>
@@ -157,6 +160,7 @@
 					:text="getNoteSummary(notification.note)"
 					:plain="true"
 					:nowrap="!full"
+					:lang="notification.note.lang"
 					:custom-emojis="notification.note.emojis"
 				/>
 			</MkA>
@@ -170,6 +174,7 @@
 					:text="getNoteSummary(notification.note)"
 					:plain="true"
 					:nowrap="!full"
+					:lang="notification.note.lang"
 					:custom-emojis="notification.note.emojis"
 				/>
 			</MkA>
@@ -183,6 +188,7 @@
 					:text="getNoteSummary(notification.note)"
 					:plain="true"
 					:nowrap="!full"
+					:lang="notification.note.lang"
 					:custom-emojis="notification.note.emojis"
 				/>
 			</MkA>
@@ -196,6 +202,7 @@
 					:text="getNoteSummary(notification.note)"
 					:plain="true"
 					:nowrap="!full"
+					:lang="notification.note.lang"
 					:custom-emojis="notification.note.emojis"
 				/>
 			</MkA>
diff --git a/packages/client/src/components/MkPoll.vue b/packages/client/src/components/MkPoll.vue
index fb5445c6c7..4a3b79f471 100644
--- a/packages/client/src/components/MkPoll.vue
+++ b/packages/client/src/components/MkPoll.vue
@@ -22,6 +22,7 @@
 					<Mfm
 						:text="choice.text"
 						:plain="true"
+						:lang="note.lang"
 						:custom-emojis="note.emojis"
 					/>
 					<span v-if="showResult" class="votes"
diff --git a/packages/client/src/components/MkPostForm.vue b/packages/client/src/components/MkPostForm.vue
index 84c3ba4cf8..1dd31ceaf8 100644
--- a/packages/client/src/components/MkPostForm.vue
+++ b/packages/client/src/components/MkPostForm.vue
@@ -147,6 +147,7 @@
 				v-model="cw"
 				class="cw"
 				:placeholder="i18n.ts.annotation"
+				:lang="language ?? undefined"
 				@keydown="onKeydown"
 			/>
 			<textarea
@@ -156,6 +157,7 @@
 				:class="{ withCw: useCw }"
 				:disabled="posting"
 				:placeholder="placeholder"
+				:lang="language ?? undefined"
 				data-cy-post-form-text
 				@keydown="onKeydown"
 				@paste="onPaste"
@@ -167,6 +169,7 @@
 				ref="hashtagsInputEl"
 				v-model="hashtags"
 				class="hashtags"
+				:lang="language ?? undefined"
 				:placeholder="i18n.ts.hashtags"
 				list="hashtags"
 			/>
@@ -178,8 +181,18 @@
 				@changeSensitive="updateFileSensitive"
 				@changeName="updateFileName"
 			/>
-			<XPollEditor v-if="poll" v-model="poll" @destroyed="poll = null" />
-			<XNotePreview v-if="showPreview" class="preview" :text="text" />
+			<XPollEditor
+				v-if="poll"
+				v-model="poll"
+				:lang="language ?? undefined"
+				@destroyed="poll = null"
+			/>
+			<XNotePreview
+				v-if="showPreview"
+				class="preview"
+				:lang="language ?? undefined"
+				:text="text"
+			/>
 			<footer>
 				<button
 					v-tooltip="i18n.ts.attachFile"
diff --git a/packages/client/src/components/MkSubNoteContent.vue b/packages/client/src/components/MkSubNoteContent.vue
index a7eb97bacb..5eb2d9f203 100644
--- a/packages/client/src/components/MkSubNoteContent.vue
+++ b/packages/client/src/components/MkSubNoteContent.vue
@@ -30,6 +30,7 @@
 			class="text"
 			:text="note.cw"
 			:author="note.user"
+			:lang="note.lang"
 			:i="$i"
 			:custom-emojis="note.emojis"
 		/>
@@ -103,6 +104,7 @@
 					:text="note.text"
 					:author="note.user"
 					:i="$i"
+					:lang="note.lang"
 					:custom-emojis="note.emojis"
 				/>
 				<MkA
diff --git a/packages/client/src/components/global/MkMisskeyFlavoredMarkdown.vue b/packages/client/src/components/global/MkMisskeyFlavoredMarkdown.vue
index 7c5d1adf95..9746e3ce3e 100644
--- a/packages/client/src/components/global/MkMisskeyFlavoredMarkdown.vue
+++ b/packages/client/src/components/global/MkMisskeyFlavoredMarkdown.vue
@@ -6,6 +6,7 @@
 		:author="author"
 		:custom-emojis="customEmojis"
 		:is-note="isNote"
+		:lang="lang"
 		class="mfm-object"
 		:class="{
 			nowrap,
@@ -28,6 +29,7 @@ const props = withDefaults(
 		customEmojis?: any;
 		isNote?: boolean;
 		advancedMfm: boolean;
+		lang?: string;
 	}>(),
 	{
 		plain: false,
diff --git a/packages/client/src/components/mfm.ts b/packages/client/src/components/mfm.ts
index a24c8cb476..04cc45ad0f 100644
--- a/packages/client/src/components/mfm.ts
+++ b/packages/client/src/components/mfm.ts
@@ -44,6 +44,10 @@ export default defineComponent({
 			type: Boolean,
 			default: true,
 		},
+		lang: {
+			type: String,
+			default: null,
+		},
 	},
 
 	render() {
@@ -558,6 +562,6 @@ export default defineComponent({
 			);
 
 		// Parse ast to DOM
-		return h("span", genEl(ast));
+		return h("span", {lang: this.lang}, genEl(ast));
 	},
 });
diff --git a/packages/firefish-js/src/entities.ts b/packages/firefish-js/src/entities.ts
index ed028efa2d..1cbdedd00b 100644
--- a/packages/firefish-js/src/entities.ts
+++ b/packages/firefish-js/src/entities.ts
@@ -150,6 +150,7 @@ export type Note = {
 	fileIds: DriveFile["id"][];
 	visibility: "public" | "home" | "followers" | "specified";
 	visibleUserIds?: User["id"][];
+	lang?: string;
 	localOnly?: boolean;
 	channel?: Channel["id"];
 	myReaction?: string;