Run tests using a particular locale and / or language (useful for SPM projects)

LocalizedTests.swift

import XCTest

class SomeTests: XCTestCase {
    override class func setUp() {
        super.setUp()
        UserDefaults.standard.set("en_US", forKey: "AppleLocale")
        UserDefaults.standard.set(["en_US"], forKey: "AppleLanguages")
        UserDefaults.standard.synchronize()
    }
    
    override class func tearDown() {
        super.tearDown()
        UserDefaults.standard.removeObject(forKey: "AppleLocale")
        UserDefaults.standard.removeObject(forKey: "AppleLanguages")
        UserDefaults.standard.synchronize()
    }
}