The primary language used for creating mobile applications on Android is Java, with Kotlin gaining popularity as a modern alternative. Java has been the longstanding official language for Android development, known for its ease of use and portability across devices. Kotlin, introduced in 2017, is designed to be fully interoperable with Java while providing more concise syntax and enhanced features, such as null safety. Both languages are supported by the Android development framework, which includes tools and libraries to streamline app creation and deployment.