Hello,
1. You can translate/rewrite all theme and plugin texts via PO file in WordPress. Here is a video tutorial that should help you translate your website texts with a Loco Translate plugin https://www.youtube.com/watch?v=D3NsDdMzsls&list=PLMw6W4rAaOgKKv0oexGHzpWBg1imvrval&index=3
Please check the video tutorial to see how to save the translation file correctly. You can remove the plugin and translations would remain. Also, translations would remain after each theme update.
2. You can try to add the widget to the top bar and add a search form into the top bar.
1. Create a sidebar in Dashboard > Sidebars;
2. Add the search widget to this Sidebar;
3. Create HTML block and add Widgetized Sidebar element, chose your sidebar;
4. Add the HTML block to the top bar of the header.
Best Regards