Things that do not have an URI, e.g. character strings are Literals. Character string are not their own separate existence, they are only a property of an Subject. Literals can be various datatypes but are usually a simple string.
Datatypes can also be used. In datatypes things can be reused that can be expressed by an XML Schema datatype. For this the namespace for XML Schema literals has to be included in the RDF document. Literals are given in quotation marks and the URI of the datatype it referring to which can be the namespace for the XML Schema datatype and with hash the string referring to.
Such strings can of course be given in different languages and it can be made clear which language it is used. For this to the string Literal a language tag can be added. Language tags are encoded in two characters (e.g. de, en, etc.).
Language tags denote the (natural) language of the text:
Literals are usually strings or can have datatypes that are expressed via XML Schema datatypes. Strings might be giving in different languages, that can be denoted via a language tag.