Task	Model	Language	N-gram-based	Embedding-based	Diversity	Ours
BLEU	ROUGE-L	METEOR	BERTScore	Distinct-1	Distinct-2	Ensemble
SG	M-BERT	en->en	2.56	18.8	0.103	0.894	0.917	0.99	31.254
de->de	2.27	13.4	0.131	0.714	0.944	0.994	34.812
fr->fr	1.38	12.7	0.201	0.715	0.945	0.997	31.209
es->es	1.81	13.5	0.121	0.72	0.955	0.996	30.825
zh->zh	4.41	25	-	0.661	1	0.124	26.354
XLM	en->en	3.71	20.5	0.107	0.895	0.968	0.995	31.701
de->de	3.02	25.3	0.14	0.729	0.966	0.995	29.758
fr->fr	4.28	25.6	0.196	0.741	0.948	0.987	27.136
es->es	3.41	24.9	0.135	0.736	0.959	0.989	27.168
zh->zh	5.71	26.3	-	0.667	0.996	0.262	26.057
mBART	en->en	4.2	21.7	0.114	0.902	0.98	1	31.65
de->de	3.64	15.5	0.142	0.733	0.982	1	34.429
fr->fr	4	16.5	0.199	0.748	0.985	1	32.808
es->es	4.21	15.6	0.14	0.741	0.982	1	31.688
zh->zh	6.52	27.3	-	0.673	0.997	0.31	26.575
mT5	en->en	2.25	17.5	0.097	0.896	0.981	0.998	31.405
de->de	1.67	11.8	0.12	0.721	0.971	0.992	35.676
fr->fr	2.44	14	0.168	0.738	0.96	0.98	32.888
es->es	2.36	13.1	0.118	0.735	0.966	0.992	31.801
zh->zh	4.62	25	-	0.664	1	0.171	26.346
SG	M-BERT	en->en	12.2	39.2	0.19	0.896	0.907	0.988	30.817
de->de	6.06	22.2	0.195	0.744	0.931	0.992	31.737
fr->fr	5.35	20.8	0.258	0.749	0.923	0.994	29.639
es->es	7.43	23.3	0.315	0.801	0.929	0.992	32.226
zh->zh	10.29	31.2	-	0.698	0.999	0.902	28.348
XLM	en->en	19.69	44.8	0.231	0.915	0.958	0.997	32.513
de->de	10.59	36.4	0.247	0.776	0.974	0.998	30.017
fr->fr	16.43	40.2	0.358	0.799	0.947	0.99	29.97
es->es	19.66	47.4	0.382	0.832	0.953	0.995	29.667
zh->zh	15.99	36.7	-	0.726	0.996	0.999	28.194
mBART	en->en	20.9	47.4	0.235	0.92	0.976	0.999	33.566
de->de	11.69	28.7	0.241	0.78	0.986	1	33.424
fr->fr	14.97	32.9	0.336	0.793	0.977	0.999	32.524
es->es	17.61	36.1	0.38	0.835	0.969	0.999	34.085
zh->zh	16.11	38.1	-	0.728	0.999	0.997	29.01
mT5	en->en	18.72	42.9	0.216	0.914	0.968	0.999	32.658
de->de	11.07	24.5	0.231	0.774	0.977	0.999	33.492
fr->fr	16.52	32.3	0.345	0.798	0.972	0.998	33.143
es->es	18.39	36.2	0.384	0.838	0.971	0.998	34.515
zh->zh	14.26	34.6	-	0.707	0.996	0.999	27.478
SG	M-BERT	en->en	14.46	36.2	0.196	0.887	0.931	0.988	30.435
de->de	6.88	16.7	0.175	0.713	0.943	0.995	31.367
fr->fr	6.59	21.1	0.22	0.727	0.89	0.984	28.491
es->es	8.69	25.4	0.264	0.748	0.892	0.988	28.126
zh->zh	11	27.8	-	0.67	0.993	0.42	26.435
XLM	en->en	15.52	34.3	0.199	0.889	0.97	0.996	31.022
de->de	7.1	20.3	0.182	0.714	0.959	0.996	30.084
fr->fr	10.25	26.6	0.279	0.742	0.915	0.988	27.814
es->es	11.4	29.3	0.284	0.756	0.912	0.994	27.954
zh->zh	11.45	24.3	-	0.659	0.976	0.614	27.165
mBART	en->en	21.78	41.9	0.231	0.905	0.984	1	33.816
de->de	9.29	22.5	0.2	0.733	0.977	0.999	31.759
fr->fr	11.86	29	0.278	0.757	0.953	0.999	29.413
es->es	13.97	32.1	0.319	0.769	0.931	0.998	29.605
zh->zh	16.73	32.9	-	0.699	0.985	0.547	28.187
mT5	en->en	15.27	35.4	0.194	0.893	0.979	0.996	32.198
de->de	7.71	18.1	0.174	0.714	0.962	0.994	31.454
fr->fr	9.8	24.7	0.245	0.74	0.941	0.992	28.479
es->es	11.73	27.5	0.277	0.753	0.925	0.993	29.504
zh->zh	12.17	26.6	-	0.667	0.986	0.52	26.145
SG	M-BERT	en->en	14.7	38.2	0.177	0.87	0.817	0.985	21.351
de->de	7.42	24.5	0.194	0.713	0.803	0.98	26.276
fr->fr	7.16	27.4	0.252	0.726	0.77	0.979	21.831
es->es	8.89	31.3	0.26	0.739	0.762	0.979	20.922
zh->zh	10.66	35	-	0.691	0.783	0.961	20.23
XLM	en->en	16.23	38.1	0.194	0.878	0.777	0.968	22.984
de->de	7.98	29.2	0.189	0.712	0.803	0.956	21.505
fr->fr	11.48	34.3	0.281	0.743	0.746	0.934	20.562
es->es	11.33	34.8	0.275	0.743	0.743	0.953	19.629
zh->zh	0.41	14.4	-	0.569	1	1	11.726
mBART	en->en	17.33	39.9	0.193	0.875	0.832	0.993	21.863
de->de	9.7	26.3	0.226	0.714	0.809	0.988	24.97
fr->fr	12.09	31.9	0.308	0.739	0.778	0.987	22.264
es->es	13.23	33.3	0.298	0.743	0.742	0.985	21.207
zh->zh	11.94	33.3	-	0.677	0.818	0.984	19.556
mT5	en->en	7.46	31	0.119	0.869	0.846	0.941	23.722
de->de	3.45	18.6	0.117	0.682	0.824	0.921	21.368
fr->fr	3.45	23.2	0.16	0.708	0.826	0.936	18.487
es->es	4.02	24.7	0.185	0.704	0.769	0.912	17.837
zh->zh	6.73	27.8	-	0.656	0.864	0.907	21.083