Add more missing language strings when importing/exporting sprite sheets

data/strings/en.ini

@@ -770,6 +770,8 @@ cancel = &Cancel
 
 [export_sprite_sheet]
 title = Export Sprite Sheet
+save_title = Save Sprite Sheet
+save_json_title = Save JSON Data
 sprite = Sprite
 sprite_tooltip = Source of sprite samples to export in the sprite sheet
 borders = Borders
@@ -975,6 +977,7 @@ horizontal_padding = Horizontal:
 vertical_padding = Vertical:
 partial_tiles = Include partial tiles at bottom/right edges
 context_bar_help = Select bounds to identify sprite frames
+layer_name = Sprite Sheet
 import = &Import
 cancel = &Cancel
 

src/app/commands/cmd_export_sprite_sheet.cpp

@@ -854,7 +854,7 @@ private:
   void onImageFilename() {
     base::paths newFilename;
     if (!app::show_file_selector(
-          "Save Sprite Sheet", m_filename,
+          Strings::export_sprite_sheet_save_title(), m_filename,
           get_writable_extensions(),
           FileSelectorType::Save, newFilename))
       return;
@@ -879,8 +879,11 @@ private:
     base::paths exts = { "json" };
     base::paths newFilename;
     if (!app::show_file_selector(
-          "Save JSON Data", m_dataFilename, exts,
+           Strings::export_sprite_sheet_save_json_title(),
-          FileSelectorType::Save, newFilename))
+           m_dataFilename,
+           exts,
+           FileSelectorType::Save,
+           newFilename))
       return;
 
     ASSERT(!newFilename.empty());

src/app/commands/cmd_import_sprite_sheet.cpp

@@ -518,7 +518,8 @@ void ImportSpriteSheetCommand::onExecute(Context* context)
     DocApi api = document->getApi(tx);
 
     // Add the layer in the sprite.
-    LayerImage* resultLayer = api.newLayer(sprite->root(), "Sprite Sheet");
+    LayerImage* resultLayer =
+      api.newLayer(sprite->root(), Strings::import_sprite_sheet_layer_name());
 
     // Add all frames+cels to the new layer
     for (size_t i=0; i<animation.size(); ++i) {