theres no easy way of controlling that. You can however set a different width for english and Polish using this CSS:
/* Max width for English site */
.main-navigation .main-nav>ul {
max-width: 700px;
}
.nav-float-right #site-navigation {
margin-left: 10px;
}
/* Max Width for Polish site */
html[lang="pl-PL"] .main-navigation .main-nav>ul {
max-width: 700px;
}
html[lang="pl-PL"] .nav-float-right #site-navigation {
margin-left: 10px;
}
Adjust the max-width and margins to control the two navigations.