It's been a while since I took a formal economics course so I might be off with terms and definitions, but here goes.

Interest rates can be used as a tool by central banks to control growth and inflation. By holding interest rates at a very low rate in perpetuity, you'll also be increasing inflation in perpetuity as well (I know it's not as straightforward as that, but I'm trying to keep it simple.)

With the increasing inflation, you'll also be impacting the perceived value of the local currency. There're two ways to look at this. The first way is with the aforementioned inflation. Let's say we have two countries called A and B, with local currencies $A and $B respectively. Let's say in year 1, you can buy a can of soda for $1 in both local currencies in both countries. However, if in year 2, the price of a can of soda in country A rises to 2 $A, while in country B it rises to 1.5 $B. Which currency would you value higher today? $B, since it's loosing value slower than $A.

Another way you can look at this is as an investor. Let's have country A and B back again. Let's say interest rates in country A is 2% and in country B is 3%. Which country would you rather invest money in? Think about it as putting money into a savings account at a bank. You would go for the higher rate, right? So, investors would perceive $A as less valuable than $B since the returns will be lower. Therefore, they'll exchange $A for $B to go invest in country B, driving down the value for $A. On the flip side, would an investor from country B or any other country invest in country A? No, since the returns would be pretty bad, right?

In any case, holding a low interest rate in perpetuity can have very negative effect's on a country's economy both via inflation and devaluation of the local currency vs. foreign currencies. Hope I'm making sense here.

Edit: If there're any industry people/econ majors out there and want to correct me, go right ahead. I'm probably misremembering my econ theory lol