I've been writing this blog since 7 months...

Here's another time-related proposition. I often hear native German speakers say "I've been working at ACME since 3 years." The correct proposition in this case is "for", "I've been working at ACME for 3 years.". Use "since" if you're refering to a particular past date. "I've worked at ACME since June of last year." is correct.

Are you reading this blog at that time?

The use of demonstrative pronouns can be tricky. If you want to refer to something that is current or happening now, use "this", not "that". I often hear Germans say (in meetings for instance) things like "We don't need to do anything at that time". Since they're refering to right now, they should say "We don't need to do anything at this time."

"At that time" is used to refer to a period of time other than the present. For example "I didn't like high school, but at that time I had no choice but to go." or "We'll go to France tomorrow and at that time will assess our options."

I wonder if persons like this blog...

While there are valid uses of the word "persons", most often one expresses the idea of more than a single person with the word "people". Today when I was signing the contract for electricity in my apartment, the very kind represenatitive asked me: "How many persons live in your flat?". While in no way ambiguous, this usage sounds odd.

Much more natural sounding would have been "How many people live in your flat?".

Did you make a good experience?

German speakers often have trouble determining when to use "to do" and when to use "to make", as a single verb is used for both these meanings in German (and Spanish, Portuguese and I'm sure many other languages). Since these verbs are so common and used in many contexts, there's no reliable usage rule that I can discern. I'll therefore call specific examples of misuse that I hear regularly.

Today, I'd like to talk about "making" an experience, as in "I have made good experiences with that approach in the past." This use of "to make" is wrong! One "has" (to have) experiences. The example sentence should have read "I have had good experiences with that approach in the past." I hope you have had a good experience with this post!

The possibility to...

My German is still too limited to figure out if this is an issue with literal translation, but I hear many Germans using constructions like this: "Do you have the possibility to call me tonight?" Using the word possibility like this will virtually always sound unnatural. It is much easier to express this sentiment using "can".

The phrase above would more naturally be expressed like this: "Can you call me tonight?" or "Would you be able to call me tonight". Instead of "I don't have the possibility of arriving at 8:00." say "I can't arrive at 8:00".

Do it until 2:00...

Prepositions are the bane of virtually all language students (those of languages that have prepositions anyway). One of the most commonly misused by Germans is "until". If something must be completed before a specified period of time, use "by", not "until"

Standard: "We need to deliver the presentation by 2:00."
Nonstandard: "We need to deliver the presentation until 2:00."

This one is particularly insidious as it doesn't typically create much ambiguity (native speakers will understand it perfectly). However, strictly speaking, to do something "until" a certain time means you do it constantly until that time. Saying "We must eat lunch until 14:00." means "We must continue eating lunch (without stopping) from now until 14:00.".

And on the one hand side...

I'm not sure if this is just a difference between British and American English, but I hear Germans commonly use the phrase "on the one hand side". To the American ear, this phrase sounds oddly redunant.

Better would be simply "on the one hand". This phrase is often used in a construction similar to this one: "On the one hand English is easy because its grammar is simple; on the other hand, it is difficult because it is so flexible.".