This paper provides a coalgebraic approach to the language semantics of regular nominal non-deterministic automata (RNNAs), which were introduced in previous work. These automata feature ordinary as well as name binding transitions. Correspondingly, words accepted by RNNAs are strings formed by ordinary letters and name binding letters. Bar languages are sets of such words modulo α-equivalence, and to every state of an RNNA one associates its accepted bar language. We show that this semantics arises both as an instance of the Kleisli-style coalgebraic trace semantics as well as an instance of the coalgebraic language semantics obtained via generalized determinization. On the way we revisit coalgebraic trace semantics in general and give a new compact proof for the main result in that theory stating that an initial algebra for a functor yields the terminal coalgebra for the Kleisli extension of the functor. Our proof requires fewer assumptions on the functor than all previous ones. * if (1) the letter a occurs in w, and (2) the first occurrence of a is not preceded by any occurrence of a. For instance, the name a is free in a aba but not free in aaba, while the name b is free in both bar strings. This yields a natural notion of α-equivalence: Definition 2.3 (α-equivalence). Let = α be the least equivalence relation on A * such that x av = α x bw for all a, b ∈ A and x, v, w ∈ A * such that a v = b w. We denote by A * /= α the sets of α-equivalence classes of bar strings, and we write [w] α for the α-equivalence class of w ∈ A * . Remark 2.4. (1) By Pitts [37, Lem. 4.3], for every pair v, w ∈ A * the condition a v = b w holds if and only if a = b and v = w, or b # v and (a b) • v = w. (2) The equivalence relation = α is equivariant. Therefore, A * /= α forms a nominal set with the group action π • [w] α = [π • w] α for π ∈ Perm(A) and w ∈ A * .The least support of [w] α is the set of free names of w.We now compose this map with the component of ε : P ufs F → GP ufs in Remark 4.19 for X = A * /= α , and then freely extend from µF = A * /= α to P ufs (µF ) = P fs (A * /= α ) using (−) ♯ (Remark C.2). This clearly yields the desired result. ⊓ ⊔