Does the Transparency Theory apply to second language acquisition (SLA)?

In my PhD research project, I investigate whether language transparency (i.e. the one-to-one relation between meaning and form)
plays a significant role in the ease or difficulty with which people learn a language, as the Learnability Hypothesis of the Transparency Theory suggests
(Hengeveld 2011; Leufkens, 2013, 2015; Hengeveld and Leufkens, 2015). The focus of this study lies on the influence of transparency on second language (L2) acquisition

The investigation is restricted to written data, collected in a longitudinal designed study in four groups of L2 learners (with no previous knowledge of their target language),
in four locations, during the period 2014 – 2016. The participants and their first and second languages are:

• Swedish native speakers studying Dutch at Stockholm University                     
• Dutch native speakers studying Swedish at the University of Amsterdam       
• Dutch native speakers studying Indonesian at Leiden University                        
• Indonesian native speakers studying Dutch at Universitas Indonesia, Jakarta 

Courses 2017 - 2018

• Swedish Language Proficiency, Culture & Modern Society, course 1 - 4 (CEFR level A1 - B1)
• Receptief taalvaardigheid Zweeds (voor studenten Deens & Noors)
• Scandinavian, course 1b - 2  ('How to understand Scandinavians')
• Taalvariatie en taalcontact in Scandinavië

Courses 2016 - 2017

• Swedish Language Proficiency, Culture & Modern Society, course 1 - 5 (CEFR level A1 - B2)
• Receptief taalvaardigheid Zweeds (voor studenten Deens & Noors)
• Scandinavian, course 1b - 2  ('How to understand Scandinavians')
• Taalkunde Scandinavisch syntaxis