Crossing Dialectal Boundaries: Building a Treebank for the Dialect of Lesbos through Knowledge Transfer from Standard M odern G reek (2025)

Abstract: This paper presents the first treebank for the dialect of Lesbos, a low-resource living Northern variety of Modern Greek (MG), annotated according to the Universal Dependencies (UD) framework. So far, the only dialectal treebank available for Greek developed with cross-dialectal knowledge transfer is an East Cretan one, which belongs to the same Southern branch as Standard Modern Greek (SMG). Our study investigates the effectiveness of cross-dialectal knowledge transfer between dialectologically less similar varieties of the same language by leveraging knowledge from SMG to annotate the Northern dialect of Lesbos. We describe the annotation process, present the resulting treebank, inject additional linguistic knowledge to enhance the results, and evaluate the effectiveness of cross-dialectal knowledge transfer for active annotation. Our findings contribute to a better understanding of how dialectal variation within language families affects knowledge transfer in the UD framework, with implications for other low-resource varieties.

## introduction the universal dependencies (ud) project (de marneffe et al., 2021) has established consistent syntactic representations across 168 languages, but non-standard varieties are underrepresented. this gap arises from challenges in text collection, the scarcity of qualified annotators, and the expertise needed to adapt existing guidelines @xcite . documenting less-used dialects not only preserves linguistic diversity but also provides valuable insights for contrastive linguistic analysis while serving as a testbed for computational approaches in data-scarce scenarios. 1 the treebank is available at https://github.com/universaldependencies/ud_greeklesbian, released as part of ud v2.16 @xcite . two ud treebanks exist for standard modern greek (smg), and recent efforts aim to develop dialectal ones, including the lesbian treebank. however, modern greek (mg) dialects remain largely unexplored. moreover, research on cross-dialectal knowledge transfer in nlp for mg is limited. to date, the only effort in this direction has focused on the east cretan dialect-an intuitively favorable case, given its relative proximity to smg as a fellow southern mg variety. this paper addresses this gap with three key contributions. (a) we present the first ud treebank for a northern mg dialect, focusing on lesbian. (b) we introduce dialect-specific annotation guidelines for lesbian and a method for integrating orthographic conventions into the annotation scheme, which is adaptable to other (northern mg) dialects without standardized orthography. (c) we extend previous research on knowledge transfer between smg and southern mg di-alects (i.e., cretan) to investigate cross-dialectal transfer between linguistically less similar varieties, specifically from smg, a southern variety, to a northern one (i.e., lesbian). in particular, we explore how the injection of linguistic knowledge can improve cross-dialectal transfer. ## related work recent work has increasingly focused on developing dialectal treebanks and exploring knowledge transfer for low-resource languages. treebanks have been created for varieties such as egyptian arabic @xcite , norwegian @xcite , occitan @xcite , and bavarian @xcite , among others. for surveys of cross-lingual transfer methods in dependency parsing, see @xcite , @xcite , @xcite , and @xcite . ## the lesbos dialect as shown in figure 1 , the lesbos dialect belongs to the northern mg dialect group, which is characterized by the so-called "northern vocalism"specifically, the raising of unstressed mid vowels /e/ and /o/ into @xcite , respectively (e.g., πιδί [piˈði] instead of smg παιδί [peˈði] 'child', κάτου [ˈkatu] instead of smg κάτω [ˈkato] 'down'), and the deletion of unstressed high vowels /i/, /u/ (e.g., these features distinguish the dialect of lesbos from southern dialects, including smg @xcite . the dialect has been shaped by extensive historical contact with italo-romance and turkish @xcite @xcite . during italo-romance rule (1355-1462), numerous loanwords and morphological elements of venetian origin were introduced, such as the diminutive suffix -ελ(ι) @xcite ] @xcite . the subsequent ottoman period (1462-1912) further enriched the dialect with turkish borrowings. around the 16th century, speakers from lesbos settled in the nearby asia minor areas of kydonies and moschonisia, where the dialects share many similarities with lesbian. after the asia minor @xcite and the treaty of lausanne (1923), refugees from these regions permanently resettled in dialectal enclaves in lesbos, resulting in a complex linguistic system on the island, characterized by intra-dialectal variation and features absent from smg. today, unlike most mg dialects, lesbian remains vital, serving as the primary means of communication on the entire island. ## the treebank this section outlines the procedure for creating the lesbian treebank. as a ud_greek treebank, it broadly follows the existing annotation guidelines for smg and adopts the same set of ufeats, upos tags, and dependency relations. accordingly, we focus on dialect-specific deviations and annotation decisions driven by dialectal features not addressed in the smg guidelines. this overview is not intended to be exhaustive (for a recent overview on the dialectal variation in lesbos, see alexelli, 2021 and the linguistic atlas of lesbos, ralli, 2019b). ## transfer experiments this section presents baseline experiments for evaluating dependency parsing performance on the lesbian treebank. the experimental setup aligns with recent approaches to nlp in low-resource settings, as surveyed by @xcite . ## discussion comparing knowledge transfer between smg and a northern (lesbian) vs. a southern (cretan) dialect reveals several key insights: the impact of dialectal distance: a southern dialect benefits more from smg knowledge transfer than a northern one, as evidenced by the superior performance of gud+cretan over gud+lesbian across all metrics. this stems from cretan's closer vocalic system to smg, while lesbian's northern vocalism introduces greater surface differences at multiple linguistic levels, demonstrating that phonological distance between northern and southern dialects limits crossdialectal transfer, regardless of orthographic consistency (see @xcite for similar results in asr for mg dialects; see also @xcite . the effectiveness of adaptation through synthetic data: our synthetic data approach significantly narrows this gap, enabling the northern dialect model to match or outperform standalone southern models across several metrics, particularly lemmatization. its effectiveness correlates with the degree of transformation: of the 25,493 tokens processed in the gud treebank, only 39.82% of surface forms and 31.82% of lemmas remained unaffected by the script, with the rest undergoing northern vocalism adaptations. these results underscore the potential for further improvements through expanded rules and additional resources such as dictionaries @xcite and parallel corpora @xcite . the importance of available resources for the standard variety: the effectiveness of (n)gud highlights the crucial role of robust standard variety resources in cross-dialectal transfer. even for less similar dialects, such as lesbian, highquality smg resources enhance performance, especially when combined with appropriate adaptation techniques. high-resource standard varieties cover greater linguistic variability, providing valuable baselines for transfer without the challenges of dialectal resource development @xcite . the role of source characteristics in knowledge transfer: the lesbian treebank integrates diverse resources, introducing variation that complicates cross-dialectal transfer but enhances representativeness @xcite . in contrast, cretan's data are more uniform as they come from a single speaker. additionally, the orthography used to transcribe cretan oral material is identical to smg orthography, which likely facilitated knowledge transfer from the smg treebank. ## conclusions in this paper, we presented the first ud treebank for a northern mg dialect (lesbian), along with tailored annotation guidelines and cross-dialectal transfer experiments. our findings suggest that effective crossdialectal knowledge transfer depends on several factors: (a) greater dialectal distance reduces transfer effectiveness; (b) the nature and diversity of source materials affect performance; (c) simple rule-based transformations of high-resource varieties can substantially improve performance for distant dialects. this research extends to other mg dialects, particularly northern varieties that share similar phonological features with lesbian. hence, the treebank provides a foundation for developing resources for other northern dialects and contributes significantly to advancing dialectal diversity in greek nlp. our work highlights an inherent paradox in cross-dialectal knowledge transfer: while we aim to leverage pre-existing resources from high-resource varieties, doing so effectively often requires developing additional dialect-specific technologies-the very situation we sought to avoid through transfer learning. similarly, a tension exists between preserving dialectal characteristics and adapting linguistic representations to enhance cross-dialectal transfer. these contradictions underscore the complex relationship between linguistic authenticity and technological pragmatism in developing nlp resources for dialectal varieties.