African multilingualism is changing the languages and identities of (urban) communities, and indeed entire nations. Sheng, a variety of Kenyan Swahili closely associated with Nairobi's urban youth, is a product of the multilingual dynamics of Nairobi city specifically, but it is also part of a continental and worldwide phenomenon. The speech code exists on a continuum of Kenyan ways of speaking Swahili within a complex and stratified multilingual society in search of a modern identity. ‘Sheng talk’ has evolved into a ‘vernacular’ that is a variety of Kenyan Swahili spoken spontaneously in informal, and some formal registers, often in response to the speakers’ audience (Bell 1984). The nature and fluidity of Sheng defies a straightforward characterization of it as a separate ‘language’ from Swahili, thus fitting in well with the concept of ‘translanguaging’, a recent term in linguistics that challenges earlier ones in the literature such as ‘code-mixing’ and ‘code-switching’ (Myers-Scotton 1993). The analytical difference between the terms lies in the discrete boundaries between languages set by the code-switching perspective, while translanguaging pays more respect to the inherent fluidity and creativity of multilingual speech codes such as Sheng or ‘Chinglish’ – English influenced Chinese (Wei 2018). There is growing recognition that ‘language’ is a process rather than an accomplished fact or closed system, and of the need to recognize the complexity of language in everyday interaction, by taking into account what have long been considered sociolinguistic factors such as setting, participants, or extra-linguistic ones such as expressions, gestures, movement, etc. Indeed, linguists such as Lüpke (2016:39) argue for the need to pay more attention to ‘the dynamic nature of language, and non-static nature of multilinguals’ language use’. Furthermore, there are language ideologies at play, or ‘beliefs about language or varieties of it, inter-subjectively held by members of the speech community’ (Milroy 2004:163). In the context we shall discuss in this book (Kenya, Nairobi) these ideologies index languages or their varieties to socio-economic status and group identities, such as Maasai (language and community), Luo (Dholuo) or Gikuyu and so on. These ideologies can also be used to create and sustain difference and group identity, or to redefine existing situations.