Linguists who study vocabulary acquisition have looked at different "coverage levels" (% of known words) to investigate the relationship between coverage and adequate comprehension. Hu and Nation (2000) found:
80% coverage no reader achieved adequate comprehension
90% coverage a few achieved adequate comprehension
95% coverage some did but most did not (Laufer 1989 agrees with this level as good for minimally acceptable comprehension)
98% coverage most readers were able to understand the text
Note this was for unassisted fiction reading.
These findings were supported in Schmitt et al. 2011. Readers understood about 50% of text at 90% coverage, and comprehension improved linearly with greater coverage.
In other words, you should shoot for reading material which you understand at least 90% of the words. Below that threshold, you won't understand enough of what you read to "pick up" the remaining vocabulary from context. Rather, you'll have the annoying process of looking up unknown words, losing your place, forgetting what you were reading, etc.
Since most of the material you want to read has vocabulary that is hard for you, you might try to focus on vocabulary FIRST. If you have a particular interest you want to read about (such as business or sports), make yourself flashcards for words related to that theme.
Another option is to look for simplified texts (such as Simple English Wikipedia) which replaces difficult words with more frequent (and thus more likely to be known) words, but I don't know the availability of these texts in languages other than English.
Hu, M., & Nation, I. S. P. (2000). Vocabulary density and reading comprehension. Reading in a Foreign Language, 23, 403–430.
Laufer, B. (1989). What percentage of text-lexis is es- sential for comprehension? In C. Lauren & M. Nordman (Eds.), Special language: From humans to thinking machines (pp. 316–323). Clevedon, Eng- land: Multilingual Matters.
SCHMITT, N. , JIANG, X. and GRABE, W. (2011), The Percentage of Words Known in a Text and Reading Comprehension. The Modern Language Journal, 95: 26-43.