Found some more places that hardcoded costume name

src/containers/costume-tab.jsx

@@ -195,7 +195,8 @@ class CostumeTab extends React.Component {
     }
     handleCameraBuffer (buffer) {
         const storage = this.props.vm.runtime.storage;
-        costumeUpload(buffer, 'image/png', 'costume1', storage, this.handleNewCostume);
+        const name = this.props.intl.formatMessage(messages.costume, {index: 1});
+        costumeUpload(buffer, 'image/png', name, storage, this.handleNewCostume);
     }
     handleFileUploadClick () {
         this.fileInput.click();

src/containers/target-pane.jsx

@@ -132,8 +132,9 @@ class TargetPane extends React.Component {
     }
     handleSpriteUpload (e) {
         const storage = this.props.vm.runtime.storage;
+        const costumeSuffix = this.props.intl.formatMessage(sharedMessages.costume, {index: 1});
         handleFileUpload(e.target, (buffer, fileType, fileName) => {
-            spriteUpload(buffer, fileType, fileName, storage, this.handleNewSprite);
+            spriteUpload(buffer, fileType, fileName, storage, this.handleNewSprite, costumeSuffix);
         });
     }
     setFileInput (input) {

src/lib/file-uploader.js

@@ -180,7 +180,8 @@ const soundUpload = function (fileData, fileType, soundName, storage, handleSoun
     handleSound(vmSound);
 };
 
-const spriteUpload = function (fileData, fileType, spriteName, storage, handleSprite) {
+const spriteUpload = function (fileData, fileType, spriteName, storage, handleSprite, costumeSuffix) {
+    const costumeName = costumeSuffix || 'costume1';
     switch (fileType) {
     case '':
     case 'application/zip': { // We think this is a .sprite2 or .sprite3 file
@@ -191,7 +192,7 @@ const spriteUpload = function (fileData, fileType, spriteName, storage, handleSp
     case 'image/png':
     case 'image/jpeg': {
         // Make a sprite from an image by making it a costume first
-        costumeUpload(fileData, fileType, `${spriteName}-costume1`, storage, (vmCostume => {
+        costumeUpload(fileData, fileType, `${spriteName}-${costumeName}`, storage, (vmCostume => {
             const newSprite = {
                 name: spriteName,
                 isStage: false,