fix(cli): preserve Language header when pushing translations (#1662)

* fix: preserve Language header when pushing translations

* refactor: remove duplicated `currentSection`

* refactor: use ternary

* refactor: remove unnecessary comments

* refactor: rename headers variable

* refactor: preserve original comment

* refactor: move comments

---------

Co-authored-by: Veronica Prilutskaya <[email protected]>

Author: ceolinwill

.changeset/quiet-clowns-bake.md

@@ -0,0 +1,5 @@
+---
+"lingo.dev": patch
+---
+
+fix language header for PO files

packages/cli/src/cli/loaders/po/index.spec.ts

@@ -367,6 +367,45 @@ msgstr "[upd] Apple"
     const result = await loader.push("en", updatedData);
     expect(result).toEqual(expectedOutput);
   });
+
+  it("should preserve existing Language header when pushing translations with metadata in first section", async () => {
+    const loader = createLoader();
+    const sourceInput = `msgid ""
+msgstr ""
+"Language: en\\n"
+"Content-Type: text/plain; charset=utf-8\\n"
+"Content-Transfer-Encoding: 8bit\\n"
+"X-Generator: next-intl\\n"
+#: hello.py:1
+msgid "Hello world"
+msgstr "Hello world"`;
+
+    const targetInput = `msgid ""
+msgstr ""
+"Language: es\\n"
+"Content-Type: text/plain; charset=utf-8\\n"
+"Content-Transfer-Encoding: 8bit\\n"
+"X-Generator: next-intl\\n"
+#: hello.py:1
+msgid "Hello world"
+msgstr ""`;
+
+    await loader.pull("en", sourceInput);
+    await loader.pull("es", targetInput);
+
+    const updatedData = {
+      "Hello world": {
+        singular: "Hola mundo",
+        plural: null,
+      },
+    };
+
+    const result = await loader.push("es", updatedData);
+
+    expect(result).toContain('"Language: es\\n"');
+    expect(result).not.toContain('"Language: en\\n"');
+    expect(result).toContain('msgstr "Hola mundo"');
+  });
 });
 
 function createLoader(params: PoLoaderParams = { multiline: false }) {

packages/cli/src/cli/loaders/po/index.ts

@@ -63,25 +63,32 @@ export function createPoDataLoader(
           const contextKey = _.keys(sectionPo.translations)[0];
           const entries = sectionPo.translations[contextKey];
           const msgid = Object.keys(entries).find((key) => entries[key].msgid);
-          if (!msgid) {
-            // If the section is empty, try to find it in the current sections
-            const currentSection = currentSections.find((cs) => {
-              const csPo = gettextParser.po.parse(cs);
-              const csContextKey = _.keys(csPo.translations)[0];
-              const csEntries = csPo.translations[csContextKey];
-              const csMsgid = Object.keys(csEntries).find(
-                (key) => csEntries[key].msgid,
-              );
-              return csMsgid === msgid;
-            });
+          
+          // If the section is empty, try to find it in the current sections
+          const currentSection = currentSections.find((cs) => {
+            const csPo = gettextParser.po.parse(cs);
+            const csContextKey = _.keys(csPo.translations)[0];
+            const csEntries = csPo.translations[csContextKey];
+            const csMsgid = Object.keys(csEntries).find(
+              (key) => csEntries[key].msgid,
+            );
+            return csMsgid === msgid;
+          });
 
+          if (!msgid) {
             if (currentSection) {
               return currentSection;
             }
             return section;
           }
           if (data[msgid]) {
+            // Preserve headers from the target file
+            const headers = currentSection
+              ? gettextParser.po.parse(currentSection).headers
+              : sectionPo.headers;
+
             const updatedPo = _.merge({}, sectionPo, {
+              headers,
               translations: {
                 [contextKey]: {
                   [msgid]: {