The high-redshift domain (mostly z ~ 2-4) allows the observation of submillimeter rotational lines of hydrides in good atmospheric windows with millimeter telescopes such as ALMA, NOEMA, etc. Strong lensed submillimeter galaxies (SMGs or dusty star-forming galaxies), discovered by Herschel, SPT, etc., provide detailed studies, which can be compared with the similar case of less luminous local ULIRGs. Emission lines generally probe the dense, warm starburst core of ULIRGs. While J~3-7 CO lines are collision excited, the excitation of H2O lines, with intensities comparable with CO, is mainly achieved through infrared pumping. Modelling such multi-line emission in a dozen of Herschel lensed SMGs allows us to constrain the conditions in their starburst core: temperature, density, temperature of IR-emitting warm dust, H2O abundance, etc. Spectacular CH° emission and absorption lines probe the turbulent gas in the regions surrounding the starburst, where turbulence is probably mostly generated by the starburst. Weaker emission lines (H2O+, HF, HCN, etc.) provide an additional diagnosis of the excitation and the chemistry in the core. Low-J emission lines of CO and CI and absorption lines (OH+, H2O, etc.) trace the molecular medium in more extended regions of the galaxies.