When we speak of - or speak - mother tongues and second (or additional) languages, as individuals, communities, and countries, that is "multilingualism." "Education" is often thought of as connected with schooling, but it also includes other modes of learning and sharing knowledge. These two concepts - multilingualism and education - along with specific attention to mother tongues, have been recurrent themes in IMLD observances over the years. And they are often discussed together - for example as "mother tongue based, multilingual education" (MTB/MLE).
"Society" seems impossibly broad, taking in pretty much everything we do. That's certainly appropriate in this context, as language and choice of languages are fundamental to our communication, interaction, and collective memory (not ignoring the tandem role of images and non-verbal.forms of communication). However I read a new and encouraging dimension to the mention of society in this year's IMLD theme: a link with sustainable development.
In an IMLD 2021 concept paper by the UNESCO Education Sector and the Organisation Internationale de la Francophonie, multilingualism is linked to the "Sustainable Development Goals’ focus on leaving no one behind" (which, by the way, actually has an acronym: LNOB). This IMLD concept paper also mentions the centrality of multilingualism for indigenous peoples' development - from which we can assume that where many languages are spoken, engaging constructively with that reality is fundamental for everyone's development.
Before coming to what I see as the key term in this year's IMLD theme - inclusion - note should be made of the action word at its beginning: "fostering." I hear this as calling out the importance of policies and planning, and the effective implementation of these. The issues of multilingualism need active attention from not only individuals, but also governments and organizations, without which we have words and no action (and in the end, no words either).
"Inclusion" turns out to be a tricky concept. Although I accept that the intent of its use in the IMLD 2021 theme is positive - the notion that languages can facilitate education and full participation in society - this term can also carry some less positive meanings. Chief among these is the implication that there is an outside and an inside, and those inside define the terms for bringing the outsiders in. There's a potential inequality there that led one writer from a community development perspective to propose abandoning the word inclusion altogether.
In the context of schools, inclusion is often (at least in the West) used in the context of students with special educational needs (and within that setting, one writer identified eleven definitions!). This does not seem to be an appropriate analogue for promoting multiple languages in education.
In the context of language and languages in Africa, the question of inclusion seems to me to become more complex. Upon independence, most African states opted to keep the colonial languages as official, rather than promoting use of one or more among their indigenous languages. This in effect put various ethno-linguistic groups within their borders at the same disadvantage (no one "inside group" controlling power). However, it also gave those who were fluent in the official languages an advantage, which is maintained through a dynamic described by Prof. Carol Myers-Scotton as "elite closure" (in other words, an there's an inside group after all).
At the same time, as Prof. Ayo Bamgbose once observed, many states operated on the paradigm that "one language always unites and many languages always divide." So in effect inclusion or exclusion in education and society have been defined to a large degree (in linguistic terms) on the basis of use of the one official language.
It is possible to find "inclusion" on more shallow level, in a group or structure that does not fully value what one brings to it, or that requires higher sacrifice from some than of others. That's as true regarding mother languages as it is regarding other aspects of culture.
While acknowledging the utility of a common language (lingua franca), the fostering of multilingualism seems to me to have the potential to shift the basis for inclusion from something centrally controlled or defined by a limited group, to a dynamic with more entry points.