Using Dual-Character Verbs When Not Necessary I am having trouble determining whether using both characters in a dual-character verb is always necessary. I am unsure about intransitive vs transitive verbs and am trying to better understand the meaning of a direct object. I notice a ton of questions on this matter so I will refrain from repeating it.

However, my question is concerned with meaning. That is, is it better to err on the side of caution and simply use both characters in a dual-character verb? I find that it is more common for dual verbs (such as 成为，知道，开始，明白) to be compact i.e. removing one character from it changes the meaning entirely, e.g. 明白 vs 明. But with others, listed below, including both characters is not required (these are transitive verbs...?). 

How is the meaning affected if the not-required character is actually included? 

Examples:

我想吃饭炒面。

他们会说话德文。

你在学习英文。

你在阅读什么书？
Some two-character verbs or verbal phrases are constructed as verb-object phrases (seperable verbs), e.g. 吃饭 (eat a meal) and 说话 (speak words). As they already have an object, you usually cannot have another object afterwards.
The first two sentences are therefore ungrammatical.

*我想吃饭炒面。=&gt; 我想吃炒面。
*他们会说话德文。=&gt; 他们会说德文。

饭 and 话 are not only unnecessary, but putting them there is simply wrong (you wouldn't say &quot;I want to eat a meal fried noodles&quot; right?).
In the case of 学习 and 阅读, these two-character verbs are pleonasms to fit words into the Chinese phonology. Individually, 学 and 习 mean roughly the same thing (learn, study) as are 阅 and 读 (read). Even when combined, they are still transitive verbal phrases that can accept objects.
However, in contemporary Chinese, one of the character is usually preferred (depending on the context and regional dialect) when there is an object and we want to simplify it. In the case of 学习 and 阅读, 学 and 读 are overwhelmingly preferred in standard Mainland Mandarin for ordinary contexts. Compare: &quot;How to study and learn&quot; and &quot;I have read and perused the many books&quot; are all fine constructions in English. As with English, their meanings when used separately have subtle differences (that I can't explain fully in this answer) and the choice of which heavily depends on phonological contexts and language register (e.g. 阅 is more literary than 读).
So, the third and fourth sentences are grammatical and they can be also simplified.

你在学习英文。 = 你在学英文。
你在阅读什么书？ = 你在读什么书？

Using 习 here is possibly acceptable (especially for certain dialects) while using 阅 here is weird and borderline ungrammatical.
The simplified sentences have the same meanings and the subtle differences are insignificant and again dependent on the broader context.