  We analyze the applicability of far-infrared fine-structure lines [CII] 158
micron, [OI] 63 micron and [OIII] 88 micron to reliably trace the star
formation rate (SFR) in a sample of low-metallicity dwarf galaxies from the
Herschel Dwarf Galaxy Survey and compare with a broad sample of galaxies of
various types and metallicities in the literature. We study the trends and
scatter in the relation between the SFR (as traced by GALEX FUV and MIPS 24
micron) and far-infrared line emission, on spatially resolved and global galaxy
scales, in dwarf galaxies. We assemble far-infrared line measurements from the
literature and infer whether the far-infrared lines can probe the SFR (as
traced by the total-infrared luminosity) in a variety of galaxy populations. In
metal-poor dwarfs, the [OI] and [OIII] lines show the strongest correlation
with the SFR with an uncertainty on the SFR estimates better than a factor of
2, while the link between [CII] emission and the SFR is more dispersed
(uncertainty factor of 2.6). The increased scatter in the SFR-L([CII]) relation
towards low metal abundances, warm dust temperatures, large filling factors of
diffuse, highly ionized gas suggests that other cooling lines start to dominate
depending on the density and ionization state of the gas. For the literature
sample, we evaluate the correlations for a number of different galaxy
populations. The [CII] and [OI] lines are considered to be reliable SFR tracers
in starburst galaxies, recovering the star formation activity within an
uncertainty of factor 2. [Abridged]
