diff --git a/tests/integration/integration_test.go b/tests/integration/integration_test.go
index e8f28105c..23567efc9 100644
--- a/tests/integration/integration_test.go
+++ b/tests/integration/integration_test.go
@@ -180,6 +180,16 @@ func (s *TestSession) GetCookie(name string) *http.Cookie {
 	return nil
 }
 
+func (s *TestSession) SetCookie(cookie *http.Cookie) *http.Cookie {
+	baseURL, err := url.Parse(setting.AppURL)
+	if err != nil {
+		return nil
+	}
+
+	s.jar.SetCookies(baseURL, []*http.Cookie{cookie})
+	return nil
+}
+
 func (s *TestSession) MakeRequest(t testing.TB, rw *RequestWrapper, expectedStatus int) *httptest.ResponseRecorder {
 	t.Helper()
 	req := rw.Request
diff --git a/tests/integration/size_translations_test.go b/tests/integration/size_translations_test.go
new file mode 100644
index 000000000..2edb0373c
--- /dev/null
+++ b/tests/integration/size_translations_test.go
@@ -0,0 +1,114 @@
+// Copyright 2024 The Forgejo Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package integration
+
+import (
+	"net/http"
+	"net/url"
+	"path"
+	"regexp"
+	"strings"
+	"testing"
+
+	"code.gitea.io/gitea/models/unittest"
+	user_model "code.gitea.io/gitea/models/user"
+	files_service "code.gitea.io/gitea/services/repository/files"
+	"github.com/PuerkitoBio/goquery"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDataSizeTranslation(t *testing.T) {
+	onGiteaRun(t, func(t *testing.T, giteaURL *url.URL) {
+		testUser := "user2"
+		testRepoName := "data_size_test"
+		noDigits := regexp.MustCompile("[0-9]+")
+		longString100 := `testRepoMigrate(t, session, "https://code.forgejo.org/forgejo/test_repo.git", testRepoName, struct)` + "\n"
+
+		// Login user
+		user2 := unittest.AssertExistsAndLoadBean(t, &user_model.User{Name: testUser})
+		session := loginUser(t, testUser)
+
+		// Create test repo
+		testRepo, _, f := CreateDeclarativeRepo(t, user2, testRepoName, nil, nil,
+			[]*files_service.ChangeRepoFile{
+				{
+					Operation:     "create",
+					TreePath:      "137byteFile.txt",
+					ContentReader: strings.NewReader(longString100 + strings.Repeat("1", 36) + "\n"),
+				},
+				{
+					Operation:     "create",
+					TreePath:      "1.5kibFile.txt",
+					ContentReader: strings.NewReader(strings.Repeat(longString100, 15) + strings.Repeat("1", 35) + "\n"),
+				},
+				{
+					Operation:     "create",
+					TreePath:      "1.25mibFile.txt",
+					ContentReader: strings.NewReader(strings.Repeat(longString100, 13107) + strings.Repeat("1", 19) + "\n"),
+				},
+			})
+		defer f()
+
+		// Change language from English to catch regressions that make translated sizes fall back to
+		// not translated, like to raw output of FileSize() or humanize.IBytes()
+		lang := session.GetCookie("lang")
+		lang.Value = "ru-RU"
+		session.SetCookie(lang)
+
+		// Go to /user/settings/repos
+		req := NewRequest(t, "GET", "user/settings/repos")
+		resp := session.MakeRequest(t, req, http.StatusOK)
+
+		// Check if repo size is translated
+		repos := NewHTMLParser(t, resp.Body).Find(".user-setting-content .list .item .content")
+		assert.True(t, repos.Length() > 0)
+		repos.Each(func(i int, repo *goquery.Selection) {
+			repoName := repo.Find("a.name").Text()
+			if repoName == path.Join(testUser, testRepo.Name) {
+				repoSize := repo.Find("span").Text()
+				repoSize = noDigits.ReplaceAllString(repoSize, "")
+				assert.Equal(t, " КиБ", repoSize)
+			}
+		})
+
+		// Go to /user2/repo1
+		req = NewRequest(t, "GET", path.Join(testUser, testRepoName))
+		resp = session.MakeRequest(t, req, http.StatusOK)
+
+		// Check if repo size in repo summary is translated
+		repo := NewHTMLParser(t, resp.Body).Find(".repository-summary span")
+		repoSize := strings.TrimSpace(repo.Text())
+		repoSize = noDigits.ReplaceAllString(repoSize, "")
+		assert.Equal(t, " КиБ", repoSize)
+
+		// Check if repo sizes in the tooltip are translated
+		fullSize, exists := repo.Attr("data-tooltip-content")
+		assert.True(t, exists)
+		fullSize = noDigits.ReplaceAllString(fullSize, "")
+		assert.Equal(t, "git:  КиБ, lfs:  Б", fullSize)
+
+		// Check if file sizes are correclty translated
+		testFileSizeTranslated(t, session, path.Join(testUser, testRepoName, "src/branch/main/137byteFile.txt"), "137 Б")
+		testFileSizeTranslated(t, session, path.Join(testUser, testRepoName, "src/branch/main/1.5kibFile.txt"), "1,5 КиБ")
+		testFileSizeTranslated(t, session, path.Join(testUser, testRepoName, "src/branch/main/1.25mibFile.txt"), "1,3 МиБ")
+	})
+}
+
+func testFileSizeTranslated(t *testing.T, session *TestSession, filePath, correctSize string) {
+	// Go to specified file page
+	req := NewRequest(t, "GET", filePath)
+	resp := session.MakeRequest(t, req, http.StatusOK)
+
+	// Check if file size is translated
+	sizeCorrent := false
+	fileInfo := NewHTMLParser(t, resp.Body).Find(".file-info .file-info-entry")
+	fileInfo.Each(func(i int, info *goquery.Selection) {
+		infoText := strings.TrimSpace(info.Text())
+		if infoText == correctSize {
+			sizeCorrent = true
+		}
+	})
+
+	assert.True(t, sizeCorrent)
+}