We had exactly this issue. We started with a central text file in our source code to manage our copy and button text. This didn't work so we just started in-lining everything. The first option wasn't creating any efficiency and was difficult to maintain effectively. In the end we have adopted a headless content management system (CMS) which is a really good option.

It allows you to store copy in a structured way. You're developers can access it as JSON while your designers and content team have a UI to update and publish the words without having to involve the tech team. Saves everyone time

Here's a blog we wrote about the decision we made

https://www.pilcro.com/blog/headless-cms

Will i be able to open and edit my old sketch files?

Thanks for your feedback, we found it really difficult to design a streamlined on-boarding experience for our desktop app. We were much more successful with our web-app (https://www.pilcro.com/appweblaunch) but there's definitely plenty of work to be done on our desktop app download page. If you have any suggestions we would love to hear them

Exciting day for @pilcrotech today