Sometimes when you are opening up your textures Pinta will be in a different language than you have as default on your Mac.
To fix this issue, you must first go to the Apple Menu, and select System Preferences.
This will open up the System Preferences menu where you will need to select "Language & Region"
From there you should see a list of all of the different languages that are on your computer. In order to fix the issue with Pinta you will need to remove all of the other languages that are there besides the language that you would like to have. To remove a language, simply click on it and the click the button below with the minus ( - ) sign on it.
You can remove multiple languages at once by clicking on the language directly below the language you want to use, scrolling down to the bottom of the list and then holding down shift and clicking on whatever language is at the bottom. Then Click on the minus symbol to remove that group of languages.
After you have removed all of the languages, close Pinta and then try to open your texture again. Pinta should now be in the language that you prefer.