"He is a slow dog, slower than a snail."
Translation:Er ist ein langsamer Hund, langsamer als eine Schnecke.
langsamer is the comparative form of langsam, but it is also the adjective form used in mixed inflection for masculine words in nominative: https://en.wikipedia.org/wiki/German_declension#Mixed_inflection.5B4.5D .
For animals in general and for wild animals, you usually use "it."
For animals you have a connection to, such as a pet dog or cat, you tend to use "he" or "she" (depending on their gender, of course).
Animal-lovers may tend to overuse "he" or "she" with all animals they see (as they feel a connection to all animals), whereas people who don't like animals may tend to overuse "it" even with pets (because they don't feel a connection with them). Basically, whenever you humanize something, you use "he" or "she" rather than "it."
This can even extend to babies; someone who particularly dislikes babies will call them "it" rather than the expected "he" or "she", which can be taken as insulting and dehumanizing the baby.
Why is "slower" translated as "langsamer"?
Because it's a predicate adjective in that position, and those don't take gender/number/case endings.
- Der Roman ist teuer. "The novel is expensive."
- Die Zeitung ist teuer. "The newspaper is expensive."
- Das Buch ist teuer. "The book is expensive."
We do not say Der Roman ist teurer, die Zeitung ist teure, das Buch ist teures in German.
We do say ein teurer Roman, eine teure Zeitung, ein teures Buch.
Attributive adjectives (before a noun) do need a gender/number/case ending.
But predicate adjectives do not.
So "the dog is slower" is der Hund ist langsamer, with only the comparative ending -er, and no gender/number/case ending.
And if you did use it attributively, the comparative comes before the gender/number/case ending, not after it; for example, ein langsameres Pferd "a slower horse". It's not ein *langsameser Pferd.
Why isn't the first part in Akkusativ?
There's no reason for it to be in the accusative case.
There's no preposition that requires the accusative case, no transitive verb that takes a direct object in the accusative case, nor anything else (e.g. a time expression in the accusative).
It's just a copular sentence "he is a slow dog", with the copula or linking verb "is" linking the subject "he" to a predicate "a slow dog". That predicate is in the nominative case in German.
If it helps, you can think of it as "he = a slow dog". They're set as equal, and are in the same case.
Here "eine Schneke" is Female nominative, right?
Right. (Mind your spelling, though -- the first e is short and so we write Schnecke with -ck- after it.)
So eine being a determiner, is taking up strong declension?
Determiners have endings all of their own -- similar to strong declension of adjectives but not identical. (In particular, they have -es in the genitive masculine or neuter, not -en like strongly-inflected adjectives would.)