If you are learning German mainly for the conversational fluency, then you in fact don't need to learn every grammar topic from the study book. You can avoid spending time and efforts learning things that are usually met only in writing or in formal settings, and instead focus on building vocabulary and mastering grammar topics that you would actually use.
The Präteritum, or simple past tense, for instance, while commonly used in written German, appears far less frequently in spoken language. Instead, the Perfekt (present perfect) is preferred in most conversational settings, even when talking about past events. Therefore, mastering the intricacies of Präteritum is not critical for initial fluency, especially since native speakers primarily use it in formal or written contexts rather than in casual conversations.
Similarly, the Futur I and Futur II tenses, which indicate future events or actions, can be approached with a more relaxed perspective in spoken German. While Futur I ("Ich werde gehen" for "I will go") is useful to know, many native speakers simply rely on the present tense with contextual clues to talk about future events. This simplification is especially common in everyday speech, where saying "Ich gehe morgen" (literally "I go tomorrow") is fully understood to mean "I will go tomorrow." Futur II, which is used to indicate actions that will have been completed by a certain future point, is even more specialized and rarely used in conversation. For example, instead of saying "Ich werde gegangen sein" (I will have gone), German speakers would more naturally find a simpler way to convey this in spoken language, or avoid the structure altogether.
Complex adjective endings, which vary according to gender, case, and number, are another area that can be set aside in the early stages. These endings play a significant role in written German but are less critical in everyday spoken interactions, where native speakers will still understand the meaning even if the endings aren’t entirely correct. Emphasis on verbs and basic sentence structure tends to communicate intent more effectively and understandably than focusing on adjective declensions.
Genitive case, often deemed crucial for correct writing and formal speech, is another element that does not require prioritization for conversational purposes. In spoken German, especially in informal settings, the genitive is often replaced by a simple construction with “von” (e.g., "das Buch von meinem Freund" instead of "das Buch meines Freundes"). While understanding genitive is necessary for reading advanced texts, it’s a case structure that learners can set aside initially without impacting their conversational fluency.
Another area that can be deprioritized is the passive voice, particularly in its more complex forms. Although passive structures are frequently encountered in written German, they are less common in everyday conversation, where simpler active constructions often suffice. Similarly, advanced relative clauses that string together multiple subordinate clauses in a single sentence, while common in formal texts and presentations, are rarely used to the same extent in spoken language. German speakers tend to break complex ideas into shorter sentences or rephrase to avoid extended clauses when speaking, making it unnecessary to master such intricate structures early on.
Finally, modal particles such as "doch," "eben," and "halt" may be interesting for understanding subtleties in German expression, but they are essentially conversational fillers. They are challenging to use correctly without considerable exposure and practice, and their absence doesn’t detract from the meaning of basic statements. Since their nuances develop naturally with increased exposure to German, focusing on these particles early on won’t be as useful as practicing core vocabulary and sentence structure.