Accurately count the non-English characters in a rich text field?

Hello!

I have a rich text field where the user can enter a marketing description. We are limited to 250 characters including spaces for this information. I have this field set up to accept a maximum of 250 characters.
To help the user, I also have a field that counts the number of characters in the field.

I'm running into an issue where any time the user enters non-English text, the character count is way off. 

For example, the German word "setzt" is counted as 149 characters. The Japanese word "ヘルプ" is counted as 146 characters. 

Is there something special I need to do with the formula to accurately count non-English characters?
Thanks!

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Karen Henke
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