I wonder to know if the formula "Flesch Reading Ease" and "Flesh Kincaid Grade Scale" can be used to measure a level of readability of reading text of which the language is not English, or in my case Indonesian?
The answer to your question is YES, even though, you may want to produce your own model of estimating the readability of Indonesian texts. In the following links, readability formulas have been applied to other languages. Hopefully, they can serve as a guideline for you to do the same in Indonesian.
We did the following experiment of text complexity as perceived by Chinese EFLs. Eight texts with different levels of difficulty (graded by familiar/unfamiliar context, vocabulary demand, sentence complexity, and passage length) were designed, each followed by five comprehension questions with different task demands. A batch of secondary two students (N=60) went through the test. Their results were assessed. We hypothesised that students' performance would show their perception of the level of difficulty. The texts were then re-arranged according to students' perception of the level of difficulty. Interestingly, students showed a different perception of difficulty with that of monolinguals. For example, if a text has a relatively familiar context, the text was judged as easier than that as assessed by the readability tools. Also, students with higher level of EFL proficiency judged text complexity differently from that of students with a lower EFL proficiency. Further experiment using Hatch (1976)'s cross-out "e" task showed that the two reader groups followed a different processing route in reading English. For students with higher proficiency, they might have skipped function words and focus more on content words for easier processing. Also, They might have linked up the concepts by their knowledge of the context in L1. Hence, vocabulary might not prove a big hindrance given that the text has a more familiar context. Students with a lower proficiency have to follow the text word by word, so vocabulary demand proved to be more significant. The present monolingual readability tools are assessed using a monolingual sample. We propose developing culturally specific EFL readability tools. feedback and further discussion.
Reza and Ori, thank a million for the answer. @Ori, your research seems interesting, can you provide me with the link to your paper, please so i can use it as my reference?
Thk you for your interest in the experimental findings. It's part of a bigger project which you may refer to in my page in the research gate. Pls quote as follows:
Wong, O.H.Y. (2015). An attempt to frame a working hypothesis of the scanning style of struggling Chinese EFLs. [unpublished manuscript]. The Educational University of Hong Kong, HK.
I do not think so, as Indonesian language which has similarity with Malays is quite different in terms of number of syllables. For example, in Malays, "gembira" refers to happy in English. But the former has 3 syllables, while the latter has only 2 syllables. Using readability formulas for Malays words can give invalid results. I would recommend you to use Khadijah Rohani Readability Index which is for Malays text.