Fun fact: the original author of Turbo Pascal, Anders Hejlsberg, went on to lead development of C# and then later TypeScript.
At work we had many, many thousands of lines manipulating strings, high and low level, and full project was over 300kLOC plus many heavy dependencies. We spent just a day or two to convert it to be Unicode capable.
Since we've had hardly any issues, and Unicode is not something we need to think about in the day-to-day.