UD Treebanks for E speranto as a natural language (2025)

Abstract: This paper describes the details of UD-based morphological and syntactic annotations on Esperanto texts to construct its small-scale UD treebank. Though it was created as an international auxiliary language, Esperanto has increasingly been studied as a natural language both in linguistics and in NLP. This paper introduces the detail of manual annotation of UD morphological and relational tags and describes how the frequencies of these tags differ across the treebanks and discusses the possibility of future research of Esperanto as a natural language.

## introduction esperanto is a constructed language created by l.l. zamenhof in 1887 for the purpose of international communication. since its creation, it has been spreading across the globe, attracting many language enthusiasts and creating a variety of communities using it as a means of communication. though it has been criticized for several reasons, it has now developed into one of the natural languages which is worthy of linguistic research and natural language processing (nlp). in this context surrounding esperanto, this paper introduces small-scale ud treebank for esperanto. this is the first contribution of esperanto to ud community (if not the first attempt to construct an esperanto treebank @xcite )), and it is expected to facilitate not only nlp research of esperanto but linguistic research in general. this paper is organized as follows: section 2 is a summary of previous studies which treat esperanto not as an artificial language but as one of the natural languages, and those which approach it from the viewpoint of nlp. section 3 summarizes the process of annotating esperanto texts with ud pos tags and ud relation tags, along with a brief description of its morphological and syntactic features. section 4 is a discussion on the issue of how ud pos tags and ud relation tags are used in different genres of esperanto texts, for the further development of future research on morphological and syntactic properties of esperanto as a natural language. as these studies indicate, esperanto in the 21 st century can be considered as a natural language which deserves linguistic investigation just like all the other natural languages, even though its status as an international auxiliary language may not be as realistic as it was intended to be when it was created in the 19 th century. ## conclusion this paper described the details of ud-based morphological and syntactic annotations on esperanto texts to construct its small-scale ud treebank. after reviewing the previous research on esperanto as a natural language, the detail of manual annotation of ud morphological and relational tags is described. then the frequencies of these tags are shown to differ across different genres of esperanto texts, and between english sentences and their esperanto translations. it is suggested that larger-scale esperanto ud treebank will open the possibility of future research which will contribute to the idea that esperanto is not an artificial language but a natural language.