In English it's normal for the sentence to start with a capital letter. In German also. Additionally, there are classes of words that are written in German with an initial capital letter.
How is it in Japanese for:
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Not many scripts/alphabets have two "cases" like the Latin script does. The Latin (English, German, French, ...), Cyrillic (Russian, Ukrainian, ...), Greek and Armenian scripts have cases (Indo-European languages), but most other scripts are unicase.
Japanese has two different phonetic alphabets (hiragana and katakana), but neither is "upper" nor "lower". They are used depending on the type of the word. For example, インターネット (the katakana word for Internet) is written like this, in all katakana, regardless of its position in a sentence. イ is always イ regardless of its position in a word. There is no such thing as "uppercase/lowercase kanji", either.
Some hiragana/katakana do have small versions, but their role is close to that of Latin diacritics. Small hiragana/katakana basically indicate a variation of the sound of the previous character. Just as Ü is a variation of U in German, ティ is a variation of テ in Japanese (note that イ is small). This is very different from the concept of uppercase/lowercase or small caps in English.
You can read an introduction of the Japanese writing system on Wikipedia.