I'm designing a feature where the user can increase or decrease a given number by tapping a PLUS or MINUS button on a mobile app. Both buttons are on the same horizontal orientation. I am unable to find a standard as to which goes on the right. I'm leaning toward putting the PLUS to the right, thinking of number-lines and other affordances of 'increase' tend to go from left to right.
In most cases, the plus should be on the right and the minus should be on the left, where we follow the X axis:
However, in some cases for example, when you are dealing with Right-To-Left languages such as Arabic, Hebrew it might require further research. But i still think it should almost always be plus right minus left.
Update regarding RTL languages:
After some research for RTL languages, in Arabic the it seems that indeed the signs are swapped so the minus is on the right and the plus is on the left, i couldn't find much regarding Hebrew but it seems for both languages it is safe and more common to use English numbers even when using the RTL language as a primary language. So unless you are specifically instructed or have a good reason to use the original numbers, you should go with English numbers