Sometimes you just need to endure a little. I remember when I started my first directory a long time ago, it was a placeholder website until I knew what I wanted to do with my domain. The next thing I knew, it exploded out of nowhere.
If I remember correctly, all I did then was to post an ad here, as well as put a link in my signature. Somehow, it made its way to get links from the VM Options and other sites that linked to my directory.
Since you are more a niche directory with a specific target market, you probably should not expect traffic to jump out of nowhere. Since you already have a target market, you must find out where you are going to get their attention. I know that social networks have already been suggested, but as they are looking for business owners, why not also put ads in forums related to business?
Start shouting about the benefits with which you can help them. I remember that on the day my directory had an Alexa rank, so whenever I promoted it, I always mentioned it in my publications. Just be ready to shout about your directory. I know you say it's not in English, etc., but hiding a link to your site keeps traffic away. You never know who hides in the forums and does not publish again, you can even find something more of your target market.
You can send your site to a directory of directories or find some sites that are linked with webmaster resources that meet the criteria of your target market. The fact of building a little more presence for your site in other sites could also give you a little more momentum. Although as you said, you lack content. If you have time to devote 5 to 10 minutes a day to your directory, you can always add some links a day to help improve it over time. You will need to find that time to dedicate yourself to it. What happens if a large influx of links is added? You will need to find time to review them, so you should be able to find time to manually add some links a day to help you complete your site a bit.
Have you also considered adding an option on your site to translate your page? I know that your main language is not English, but could you always offer an option to translate the page to different languages? The only drop in the boxes is that you will also get some shipments in English, but it is another option to boost your target market. Could you give us more information about the niche of your directory so we can give you some more detailed suggestions?