My parents moved to Austria from Poland in 1988 while my mom was pregnant with my twin and me.
From my birth on until I went to kindergarten at 4 years (I had to skip a year, because of my asthma and allergies that made it impossible for me to be out in the sun as I would simply collapse) I didn't speak German at all. We did spend a little time with the neighbors kids, but because I was very sick as a kid I know it was very little interaction.
So I started to learn German when I was about 4 years in Kindergarten through playing with my peers and talking to my caretakers. Throughout my life I never had any real problems with the language. The only things that I did come across, were not knowing German stories and tales as my parents would read Polish ones to us, which in hindsight is not really a big issue. I learned about them when we worked through them in high school, so I might not know all of them, but I know the most important ones and if I really wanted to, I could always read up on them now.
When I was 11 years old I started to learn English as well in school. My teacher thought I had a talent for languages and was very proud to have my sister and me in her class as we seemed to grasp what she tried to teach us very quickly.
In high school I had to take another language, besides English, and I picked French. I was fine at the beginning, but when we got introduced to different tenses I just couldn't keep up and I wasn't really good at it. However, we took a trip to France in 7th grade (I was 17) and we lived with a family for a week - I had no problem talking to them and understanding what they wanted from me.
So after this long introduction, here is my main point:
My sister has recently had a baby (I say recently, but she is already turning a year next month.) and she is forbidding my mom to speak Polish with her. She says that if she spoke Polish with my niece, she would not have enough German influence around her to learn to speak the language properly and I found out that it is not what she wants, it is in fact her husbands biggest concern. At the beginning, when Lilly was born, she spoke Polish with her everyday, but then her husband permitted her to speak it, because he was worried she would never learn German.
I was appalled. I have so many scientific papers that say that kids can easily learn more than one language and my experience (and hers aswell!) should be proof of that, yet she is robbing my parents of their chance to speak with their niece in their mother tongue.
When I told my man about this, he said he thinks it is a sad decision on their part. He appreciates that I can speak more than just one language and in fact expects me to teach our future kids both. I had to tell him that you can only do one language per person to not confuse the baby and since my German is better than my Polish, I would use that to speak to them and he said, I quote:
Wouldn't every parent want their kid to have the possibility to learn more than one language?
and
Your parents better spend a lot of time with their grandchildren so they can teach her Polish!
This was something that was very dear to my heart. My English is never going to be perfect, ever, and I never wanted to give up on German and Polish either, they are my past and my present and so I am happy to say that this is my fiance, who is supportive of this and wants our kids to have the opportunity to speak to their uncles, aunts and grandparents in their main language.
It makes me sad to see my big sister yell at my mom when she swaps between German and Polish. I just know that when I have kids, I will not do the same.
My sister's husband speaks German and a little tiny bit of English, because we're all required to learn it in school, but that's it. Maybe it is this fact that he doesn't want it around his daughter. I just feel like it makes no sense, because like you said, OperaDiva, they live in Austria, both parents speak German, her brother speaks German, all their friends and acquaintances who visit very often speak German and he still thinks she wouldn't hear enough. I also think the real issue here, and that is something they won't admit or say, is that her brother's written German is pretty bad and they worry that this is because my mom spoke Polish to him, but they totally disregard that he has been pushed from one parent to another when my sister and her ex-husband were in the process of leaving one another and getting divorced without having any consideration for his work done at home for school. She would simply not do it with him, she would tell him to do it himself and his father wasn't any better, he simply told him to not do it - no wonder he didn't learn anything!!
What bothers me the most, is the way my big sister reacts to my mom.. it's just awful and their reasoning makes no sense. I have been called a "know-it-all teacher" by my big sister before, so I refrain from giving her any tips, but I have asked many of my professors about the issue to help her deal with it. She doesn't want to hear any of it.
I guess it just makes me appreciate my man more, to know that our future children will be given this opportunity.
Sorry, I am speculating here, but it could be useful to try and see things from her perspective. Maybe when things quiet down in their family, their relationship can be more stable and your niece won't be too old to start learning Polish for many years to come
One different note, my SO and I met this american guy once who was also married with a romanian woman and he told my husband that he found the langauge difficult to learn and he gave up, but now his wife and his kids can talk and he has no idea what goes on. So he looked at my SO and said, quite seriously but also in a funny way: "Buddy, I am telling ya', if ya' know what's good for you.. GET WITH THE PROPGRAM!" I don't know if my SO actually will, but it would help.