## 1 Introduction  
The definition of \"mother tongue\" varies across different sources and continues to evolve to encompass the nuances of language use by individuals. One commonly accepted definition is that it refers to the language a person learns through their interactions with family and society during the early years of their life [1]. According to UNESCO, there are over 7000 known mother tongues in the world, with approximately 3000 of them facing the risk of extinction in the near future [2]. Hundreds of millions of people speak some mother tongues, such as Chinese, Hindi, Spanish, English, Arabic, Japanese, and Russian. Others like Turkish, Korean, French, German, Bengali, and Italian also have many speakers globally. As the Internet continues to expand its reach across the globe, becoming accessible even to less economically developed populations, the diversity of languages used in the digital world is also increasing. English used to be the dominant language on the Internet; however, this is changing as more non-English speakers access online resources. The ability of people from different countries and cultures to communicate and share information in their mother tongue has resulted in a proliferation of diverse languages being used on the Internet. The exponential increase in the global Internet user base has expanded the market reach for companies; however, the diverse linguistic landscape online presents a formidable challenge in effectively engaging with people from different language backgrounds. Communicating and marketing successfully with individuals speaking different languages is crucial to understanding and utilising their mother tongue. The mother tongue of Internet users serves as a defining characteristic, and knowledge of this aspect can be leveraged in various ways to enhance business strategies and user experiences. Understanding a user's mother tongue can have practical applications in various domains. For instance, Internet service providers (ISPs) can customise their services to align with users' language preferences, thereby enhancing user experience. Similarly, online businesses can improve their targeted advertising strategies by considering customers' mother tongues, as different language preferences may entail distinct consumer needs. Additionally, in digital forensics, knowledge of a suspect's mother tongue can serve as valuable evidence in criminal investigations, allowing investigators to narrow the pool of potential suspects. Investigators often need to sift through substantial amounts of data and digital evidence to identify perpetrators when dealing with cybercrimes. Information about the suspect's mother tongue can help focus investigative efforts on a smaller subset of suspects. Another practical application is automatically modifying the interface of a website or application based on the user's mother tongue, making it more accessible and user-friendly, thus enhancing user satisfaction and engagement. Overall, leveraging the knowledge of a user's mother tongue can have diverse applications in fields such as ISP services, targeted advertising, digital forensics, and website/application design to enhance user experiences and streamline processes. This paper aims to identify the mother tongue of an unknown user by leveraging KD, which involves analysing how individuals type on a keyboard, including factors such as timing, speed, and pressure of key usage. KD has been utilised in various applications such as authentication, biometrics, and user behaviour analysis [3], and offers a promising avenue for research in diverse fields, ranging from cybersecurity to psychology. The ability to identify individuals based on their unique typing patterns has significant implications for authentication, user behaviour analysis, and other related areas [4]. The remainder of this paper is organised as follows: The next section provides a comprehensive review of the relevant literature that contextualises the topic of this study.