This paper presents the phonological, morphological, and syntactic
distinctions between formal and informal Persian, showing that these two
variants have fundamental differences that cannot be attributed solely to
pronunciation discrepancies. Given that informal Persian exhibits particular
characteristics, any computational model trained on formal Persian is unlikely
to transfer well to informal Persian, necessitating the creation of dedicated
treebanks for this variety. We thus detail the development of the open-source
Informal Persian Universal Dependency Treebank, a new treebank annotated within
the Universal Dependencies scheme. We then investigate the parsing of informal
Persian by training two dependency parsers on existing formal treebanks and
evaluating them on out-of-domain data, i.e. the development set of our informal
treebank. Our results show that parsers experience a substantial performance
drop when we move across the two domains, as they face more unknown tokens and
structures and fail to generalize well. Furthermore, the dependency relations
whose performance deteriorates the most represent the unique properties of the
informal variant. The ultimate goal of this study that demonstrates a broader
impact is to provide a stepping-stone to reveal the significance of informal
variants of languages, which have been widely overlooked in natural language
processing tools across languages.

探讨波斯语（Persian）的正式形式和非正式形式之间的音韵、形态和句法区别，提出正式形式的树库在计算模型转换到非正式形式表现糟糕的问题，并开发了基于通用依赖理论的非正式波斯语树库，研究表明现有依赖树库训练的依存分析器在跨越两个领域时表现不佳，而非正式形式的语言的独特特征更容易出现错误。