How much slower is reading in a second language?

These findings are reported in the review's section on non-native readers. The review explicitly notes that the novel study's statistics do not permit a directly comparable absolute WPM estimate. Keeping that qualification matters: the 17% should not be used as an adjustment factor for every language learner. Brysbaert, 2019

Why proficiency matters more than the label L2

Second-language experience changes the processing of words, including sensitivity to how frequently they occur. The Whitford and Titone study examines those effects with eye movements during paragraph reading. Two people with the same first and second languages can therefore face different processing demands because their exposure and proficiency differ. Whitford et al., 2012

Vocabulary knowledge is part of this context. Coverage research asks how many words in a particular text the reader knows, while vocabulary-size estimates depend on whether forms, lemmas or families are counted. A raw word-count estimate cannot by itself predict fluent reading of every text. Nation, 2006 Brysbaert et al., 2016

Why WPM cannot rank languages directly

Different languages use different numbers of written words to express comparable information. Word length, morphology and writing systems influence the unit being counted. The reading-rate and eye-movement reviews therefore do not support interpreting a lower WPM in another language as lower intelligence or slower general thinking. Brysbaert, 2019 CLIFTON et al., 2015

Text difficulty and task instructions change the result

Reading for pleasure, studying and locating a fact are different tasks. Eye-movement research shows how word difficulty and comprehension demands affect visual sampling. A familiar story and an unfamiliar technical article should not be treated as interchangeable probes of one fixed reading speed. Rayner, 1998 CLIFTON et al., 2015

Regressions can help a reader resolve uncertainty. Experimental evidence that restricting rereading harms comprehension cautions against treating every pause or return in L2 as an inefficiency to suppress. Some of the extra time may serve understanding. Schotter et al., 2014

Can practice close the gap?

The reviews support the importance of language experience and efficient word recognition, but they do not establish a universal number of hours needed to match first-language reading. Nor do these cross-study examples yield a valid age-by-sex training forecast. Improvement should be measured within comparable tasks and language conditions. Rayner et al., 2016 Whitford et al., 2012

Use suitable unfamiliar material, check comprehension and record the language and purpose of each timing. Reading easier text faster can be useful, but it does not by itself demonstrate that reading ability increased by the same amount on harder material. A meaningful comparison keeps the difficulty and goal reasonably comparable. Brysbaert, 2019 Nation, 2006

The practical answer is therefore a range of possibilities, not a single multiplier. The published 139, 61 and 17% results illustrate how much the population and task matter. They should help interpret variation, rather than create a new universal learner threshold. Brysbaert, 2019