求翻译：这些研究虽取得了一定的研究成果, 但未能真正回答二语词汇能力发展停滞的原因这一问题。因为这些研究只局限于词汇能力发展的外部因素, 而忽略了对词汇能力发展的内部因素是什么意思？

Although these studies have made some research but could not really answer the second language vocabulary ability stagnation causes this problem. Because these studies limited vocabulary ability development of the external factors, while ignoring the internal factors vocabulary ability development

Although these studies have made a certain amount of study results, but was unable to really answered 2 language vocabulary development is stagnant because of this problem. Because these studies are only limited to vocabulary development, to the neglect of the external factors in the development of

Although these research has obtained certain research results, but has not been able to reply truly two language glossary ability development stagnates reason this question.Because these research only limits to the glossary ability development exterior factor, but has neglected to the glossary abili

Despite a certain amount of research findings from these studies, but did not really answer of second language vocabulary development stagnation causes this problem. Because these studies are only confined to the development of lexical competence of external factors, rather than internal factors on

Although the research makes certain research results, fail to really answer two language vocabulary abilities and develop this question of the stagnant reason. Because the research is only limited to the external factor of ability development of vocabulary, and neglected the internal factor to abili